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#### Question 1:

Solid sodium bicarbonate was placed on a strip of pH paper. The colour of the strip:
(1) turned blue
(2) did not change
(3) turned green and suddenly yellow
(4) turned light pink

Color of the strip didn't change because pH paper strip changes its color when the substance to be tested is in the ionic form. But, here the given substance, sodium bicarbonate is in solid form.

Hence, the correct answer is option 2.

#### Question 2:

When dilute hydro-chloric acid is added to granulated zinc placed in a test tube, the observation made is
(1) the surface of the metal turns shining
(2) the reaction mixture turns milky
(3) odour of chlorine is observed
(4) a colourless and odorless gas evolves with bubbles

When dilute hydrochloric acid is added to granulated zinc, colorless and odorless hydrogen gas is evolved with bubbles.
$2\mathrm{HCl}\left(\mathrm{l}\right)+\mathrm{Zn}\left(\mathrm{s}\right)\to \mathrm{ZnCl}{}_{2}\left(\mathrm{aq}\right)+{\mathrm{H}}_{2}\left(\mathrm{g}\right)$

Hence, the correct answer is option 4.

#### Question 3:

When an aluminium strip is kept immersed in freshly prepared ferrous sulphate solution taken in a test tube, the change which is observed is:
(1) light green solution slowly turns colourless
(2) the lower end of the test tube becomes slightly warm
(3) a colourless gas with smell of burning sulphur is observed
(4) light green solution changes to blue

Aluminium is more reactive than iron hence will displace iron from the solution, so when an aluminium strip is kept immersed in freshly prepared light green colored ferrous sulphate solution, aluminium displaces iron from iron sulphate and forms blue colored aluminium sulphate.
$2\mathrm{Al}\left(\mathrm{s}\right)+3{\mathrm{FeSO}}_{4}\left(\mathrm{aq}\right)\to {\mathrm{Al}}_{2}\left({\mathrm{SO}}_{4}{\right)}_{3}\left(\mathrm{aq}\right)+3\mathrm{Fe}\left(\mathrm{s}\right)$

Hence, the correct answer is option 4.

#### Question 4:

The description which most approximately suits sulphur dioxide gas is that it is colourless and :
(1) insoluble in water
(2) has pungent and suffocating odour
(3) lighter than air
(4) has smell of rotten eggs

Sulfur dioxide is a colorless gas. It has a pungent and suffocating odour. Inhaling it can cause inflammation in eyes, headache, and if inhaled for a long time it can cause death.

Hence, the correct answer is option 2.

#### Question 5:

Ethanoic acid was added in drops to water and it was noticed that:
(1) the acid formed a separate layer on the top of water
(2) water formed a separate layer on the top of the acid
(3) a clear and homogeneous solution was formed
(4) a pink and clear solution was formed

When ethanoic acid was added in drops to water it formed a clear and homogenous solution due to the formation of intermolecular hydrogen bonding.

​Hence, the correct answer is option 3.

#### Question 6:

A colourless liquid sample was tested with pH paper strip. The colour of the strip changed to reddish pink. The sample could be :
(1) tap water
(2) sodium hydroxide solution
(3) distilled water
(4) ethanoic acid solution

Bases turn red litmus paper to blue and acids turn blue litmus paper to red. Here the colour of litmus paper changes to reddish pink so the colourless solution must be acid. Ethanoic acid can convert blue litmus paper to reddish pink.

Hence, the correct answer is option 4.

#### Question 7:

Ethanoic acid was added to sodium hydrogen-carbonate solution and the gas evolved was tested with a burning splinter. The following four observations were reported:
(a) The gas burns with the pop sound and the flame gets extinguished.
(b) The gas does not burn but the splinter burns with a pop sound.
(c) The flame extinguishes and the gas does not burn.
(d) The gas burns with a blue flame and the splinter burns brightly.

The correct observation is reported in :
(1) (a)
(2) (b)
(3) (c)
(4) (d)

When ethanoic acid is treated with sodium hydrogen carbonate then carbon dioxide gas evolves which produce effervescence. Flame extinguishes and gas does not burn.
${\mathrm{NaHCO}}_{3}+{\mathrm{CH}}_{3}\mathrm{COOH}\to {\mathrm{CH}}_{3}\mathrm{COONa}+{\mathrm{CO}}_{2}+{\mathrm{H}}_{2}\mathrm{O}$

Hence, the correct answer is option 3.

#### Question 8:

Which one of the following setups is the most appropriate for the evolution of hydrogen gas and its identification?

(1) (a)
(2) (b)
(3) (c)
(4) (d)

When zinc reacted with dilute sodium hydroxide, hydrogen gas is evolved, which can be easily tested in the second test tube as there is proper space for the gas to be tested.
$\mathrm{Zn}\left(\mathrm{s}\right)+\mathrm{NaOH}\left(\mathrm{aq}\right)\to {\mathrm{Na}}_{2}{\mathrm{ZnO}}_{2}\left(\mathrm{aq}\right)+{\mathrm{H}}_{2}\left(\mathrm{g}\right)$

Hence, the correct answer is option 2.

#### Question 9:

Four students A, B, C and D noted the initial colour of the solutions in beakers I, II, III and IV. After inserting zinc rods in each solution and leaving it undisturbed for two hours, noted the colour of each solution again.

They recorded their observations in the form of a table given below:

 Student Colour of the solution I II III IV A Initial Final Colourless Colourless Colourless Colourless Light green Colourless Blue Colourless B Initial Final Colourless Colourless Light yellow Colourless Light green Light green Blue Colourless C Initial Final Colourless Light blue Colourless Colourless Light green Colourless Blue Light blue D Initial Final Light green Colourless Colourless Colourless Light green Dark green Blue Colourless

Which student noted the colour change in all the four beakers correctly?

For I, zinc rod is dipped in aluminum sulphate, but zinc is less reactive than aluminum so, no reaction will take place.
For II, zinc rod is dipped in zinc sulphate, here no reaction will take place as zinc rod is dipped in zinc solution.
For III, zinc rod is dipped in ferrous sulphate, zinc is more reactive than ferrous sulphate. Ferrous sulphate is of light green color which on reaction with zinc gives zinc sulphate which is colorless.
$\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{FeSO}}_{4}\left(\mathrm{aq}\right)\to {\mathrm{ZnSO}}_{4}\left(\mathrm{aq}\right)+\mathrm{Fe}\left(\mathrm{s}\right)$
For IV, zinc rod is dipped in copper sulphate, zinc is more reactive than Copper sulphate. Copper sulphate is of light blue color which on reaction with zinc gives zinc sulphate which is colorless.
$\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{CuSO}}_{4}\left(\mathrm{aq}\right)\to {\mathrm{CuSO}}_{4}\left(\mathrm{aq}\right)+\mathrm{Fe}\left(\mathrm{s}\right)$
So, the observations made by student A are correct.

Hence, the correct answer is option 1.

#### Question 10:

Four gas jars filled with sulphur dioxide gas were inverted into troughs of water by four students and the following observations and inference were reported:

(a) Water did not enter the gas jar and sulphur dioxide is insoluble in water.
(b) A Small amount of water entered the gas jar slowly and sulphur dioxide is sparingly soluble in water.
(c) Water rushed into the gas jar and sulphur dioxide is highly soluble in water.
(d) Water did not enter the gas jar and sulphur dioxide is soluble in water.

The correct set of observations and inference drawn is reported in :
(1) (a)
(2) (b)
(3) (c)
(4) (d)

Sulphur dioxide is sparingly soluble in water, so it will slowly rise up the water level in the jar.
${\mathrm{SO}}_{2}\left(\mathrm{g}\right)+{\mathrm{H}}_{2}\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{H}}_{2}{\mathrm{SO}}_{3}\left(\mathrm{aq}\right)$

Hence, the correct answer is option 2.

#### Question 11:

The colour of the pH paper strip turned red when it was dipped into a sample. The sample could be :
(1) dilute sodium bicarbonate solution
(2) tap water
(3) dilute sodium hydroxide solution
(4) dilute hydrochloric acid

Acids convert blue litmus paper to red. So, out of the given options dilute hydrochloric acid will turn blue litmus to red.

Hence, the correct answer is option 1.

#### Question 12:

A Drop of colourless liquid was placed on blue litmus paper. The litmus paper turned red. The liquid could be :
(1) dilute hydrochloric acid
(2) dilute sodium hydroxide solution
(3) distilled water
(4) sodium bicarbonate solution

Acids turn blue litmus paper to red, so among the following options dilute hydrochloric acid will turn blue litmus to red.

Hence the correct option is 1.

#### Question 13:

A piece of granulated zinc was dropped into copper sulphate solution. After some time, the colour of the solution changed from :
(1) light green to blue
(2) blue to colourless
(3) light green to colourless
(4) bule to yellow

Zinc is more reactive than copper, as zinc displaces copper from the copper sulphate and form zinc sulphate, as a result, the blue colour solution turns colourless.
$\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{CuSO}}_{4}\left(\mathrm{aq}\right)\to {\mathrm{ZnSO}}_{4}\left(\mathrm{aq}\right)+\mathrm{Cu}\left(\mathrm{s}\right)$

Hence, the correct answer is option 2.

#### Question 14:

When sulphur dioxide gas is passed through acidified potassium dichromate solution, the colour of the solution changes from :
(1) orange to yellow
(2) orange to green
(3) green to orange
(4) yellow to green

When sulphur reacts with orange coloured acidified potassium dichromate solution, it changes the orange coluored solution to green due to the formation of green coloured chromium sulphate.

Hence the correct option is 2.

#### Question 15:

The odour of ethanoic acid resembles with :
(1) tomato juice
(2) kerosene
(3) orange juice
(4) vinegar

Vinegar is a 15-20% aqueous solution of ethanoic acid that's why its odor resembles with it.

Hence, the correct answer is option 4.

#### Question 16:

Which one of the following solutions would you use to test the pH of a given sample?
(1) blue litmus solution
(2) red litmus solution
(3) universal indicator solution
(4) mixture of red and blue litmus solution

Universal indicator is made up of several solutions having a wide range of pH values, to indicate the acidity and alkalinity of solutions. So, to test a sample we would use a universal indicator.

Hence the correct option is 3.

#### Question 17:

5 mL of dilute acetic acid were added to 5 mL of water and mixture was shaken for one minute. It was observed that :
(1) the turbidity appeared in the test tube
(2) the acid formed a separate layer at the bottom
(3) water formed a separate layer at the bottom
(4) a clear solution was formed

When dilute acetic acid was added to water, a clear homogeneous solution is formed due to the presence of intermolecular hydrogen bonding.

Hence, the correct answer is option 4.

#### Question 18:

Four set ups as given below were arranged to identify the gas evolved when dilute hydrochloric acid was added to zinc granules. The most appropriate set up is :

(1) I
(2) II
(3) III
(4) IV

When zinc is treated with dilute hydrochloric acid, hydrogen gas is liberated from the solution. Only from setup 4 hydrogen gas can easily be liberated.
$\mathrm{Zn}\left(\mathrm{s}\right)+2\mathrm{HCl}\left(\mathrm{aq}\right)\to {\mathrm{ZnCl}}_{2}\left(\mathrm{aq}\right)+{\mathrm{H}}_{2}\left(\mathrm{g}\right)$

Hence the correct option is 4.

#### Question 19:

Which two equipments would you choose to prepare and collect sulphur dioxide gas in the laboratory?

(1) I and IV
(2) I and III
(3) II and IV
(4) II and III

To prepare and collect sulphur dioxide, fit a clamp at the top, and keep the cork in position(withstanding the pressure of SO2 gas) as in setup I, and a tube is required for SO2 to flow into the collector as in setup IV.

Hence, the correct answer is option 1.

#### Question 20:

Aqueous solutions of zinc sulphate and iron sulphate were taken in the test tubes I and II by four students. A, B, C and D. Metal pieces of iron and zinc were dropped in the two solutions and observations made after several hours and recorded in the form of a table as given below:

 Observation by Metal Solution Colour change of solution Deposit/Residue obtained A Fe ZnSO4 turned green silvery grey coating Zn FeSO4 no change no change B Fe ZnSO4 no change black residue Zn FeSO4 colour faded grey coating C Fe ZnSO4 no change no change Zn FeSO4 turned colourless black residue D Fe ZnSO4 no change grey residue Zn FeSO4 no change black residue
The correct reporting has been made observations reported by the student :
(1) A
(2) B
(3) C
(4) D

When iron is treated with zinc sulfate, no reaction takes place because iron is less reactive than zinc.
When zinc is treated with iron sulphate, the green colour solution becomes colourless and black residue of iron is obtained.
So observations made by student C are correct.

Hence, the correct answer is option 3.

#### Question 21:

The 'set up', used in the laboratory, to collect sulphur dioxide, is that shown in figure :

(1) I
(2) II
(3) III
(4) IV

SO2 gas is sparingly soluble in water; when SO2 gas is passed in water, it is converted to H2SO3.

Hence, the correct answer is option 3.

#### Question 22:

A student adds a few drops of the universal indicator to a solution of dilute hydrochloric acid in the way shown here. He would observe that the colour of the solution changes form colourless to :

(1) red
(2) yellow
(3) violet
(4) green

Universal indicator is used to test the pH of unknown solutions, acids give red color with universal indicator. Hence when the universal indicator is dropped in hydrochloric acid, it gives red color.

Hence, the correct answer is option 1.

#### Question 23:

When zinc metal is heated with caustic soda solution, the gas evolved is :
(1) hydrogen
(2) carbon dioxide
(3) oxygen
(4) hydrogen choride

When Zn metal is heated with caustic soda(NaOH) solution, then hydrogen gas evolves.
$\mathrm{Zn}\left(\mathrm{s}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)\to {\mathrm{Na}}_{2}{\mathrm{ZnO}}_{2}\left(\mathrm{aq}\right)+{\mathrm{H}}_{2}\left(\mathrm{g}\right)$

Hence, the correct answer is option 1.

#### Question 24:

Four students observed the colour and odour of acetic acid and its reaction with sodium hydrogencarbonate. They tabulated their observations as given below.

 Student Colour of acetic acid Odour of acetic acid Action with sodium hydrogencarbonate A B C D blue colourless light green  light brown fruity smell of vinegar odourless rotten eggs gas evolves without bubbles effervescence gas evolves without bubbles effervescence
The correct set of observation is that of student:
(1) A
(2) B
(3) C
(4) D

Ethanoic acid is commonly known as acetic acid. It is colorless gas having a smell of vinegar. On reaction with sodium hydrogen carbonate, it gives carbon dioxide which gives effervescence.
${\mathrm{CH}}_{3}\mathrm{COOH}\left(\mathrm{aq}\right)+{\mathrm{NaHCO}}_{3}\left(\mathrm{aq}\right)\to {\mathrm{CH}}_{3}\mathrm{COONa}\left(\mathrm{aq}\right)+{\mathrm{H}}_{2}\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{CO}}_{2}\left(\mathrm{g}\right)$

Hence the correct option is 2.

#### Question 25:

A student takes Cu, Al, Fe and Zn pieces separately in four test tubes labelled as I, II, III, and IV respectively. He adds 10 mL of freshly prepared ferrous sulphate solution to each test tube and observes the colour of the metal residue in each case.

He would observe a black residue in the test tubes :
(1) (I) and (II)
(2) (I) and (III)
(3) (II) and (III)
(4) (II) and (IV)

Copper is reactive than iron. Therefore, no reaction takes place when ferrous sulphate solution is added to copper containing test tube. So, in case one nothing will happen.
When ferrous sulphate is added to aluminium containing test tube then following reaction takes place:
$2\mathrm{Al}\left(\mathrm{s}\right)+3{\mathrm{FeSO}}_{4}\left(\mathrm{aq}\right)\to {\mathrm{Al}}_{2}\left({\mathrm{SO}}_{4}{\right)}_{3}\left(\mathrm{aq}\right)+3\mathrm{Fe}\left(\mathrm{s}\right)$
So the green colour of FeSO4 disappears. Iron metal is settling down at the bottom of the test tube.
When ferrous sulphate is added to the iron-containing solution, then no change will be observed since metal is same, i.e. iron.
When ferrous sulphate is added to the zinc-containing test tube then the following reaction takes place:
$\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{FeSO}}_{4}\left(\mathrm{aq}\right)\to {\mathrm{ZnSO}}_{4}\left(\mathrm{aq}\right)+\mathrm{Fe}\left(\mathrm{s}\right)$
So the green colour of FeSO4 disappears Fe metal is settling down at the bottom of the test tube.

Hence the correct option is 4.

#### Question 26:

Four students, (A), (B), (C) and (D) observed the colour and solubility of iron, sulphur and iron sulphide in carbon disulphide. The tick mark (✓) represents 'soluble', and cross mark (×) represents 'insoluble' in carbon disulphide. Their observations are tabulated below :

 Student Colour Solubility in carbon disulphide Fe S FeS Fe S FeS (A) (B) (C) (D) Yellow Silvery Grey Silvery Silvery Orange Yellow White Greyish silver Reddish brown Greyish black Silvery white (✓) (×) (×) (✓) (×) (✓) (✓) (×) (✓) (✓) (×) (×)
The student, who correctly reported the observation, is student :
(1) (A)
(2) (B)
(3) (C)
(4) (D)

When iron is extracted, it is of grey color, and when it is reacted with sulfur, they form black iron sulfide. And sulfur is of yellow.
From the following table, it can be concluded that only sulfur is soluble in carbon disulfide solution.
So student C correctly reported the observation.
Hence, the correct answer is option 3.

#### Question 27:

A student adds a few drops of the universal indicator solution to a dilute solution of sodium hydrogencarbonate taken in a test-tube. Which of the following colour would he observe?

(1) blue
(2) green
(3) mustard
(4) yellow

Universal indicator is used to check the pH of unknown solutions. Acids give red color on the addition of universal indicator while bases give blue color. So sodium hydrogen carbonate is a base so it will turn the colorless solution to blue.

Hence the correct option is 1.

#### Question 28:

A student strongly heats hydrated ferrous sulphate salt in a dry test-tube. He would observe a :
(1) yellow residue
(2) brown residue
(3) light green residue
(4) white residue

Ferrous sulfate is basically a hydrated salt and blue-green in color. On heating in a dry test tube, it will lose its water molecules and become anhydrous. Decomposition reaction of ferrous sulfate is given below:
$2{\mathrm{FeSO}}_{4}\left(\mathrm{s}\right)\stackrel{∆}{\to }{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}\left(\mathrm{s}\right)+{\mathrm{SO}}_{2}\left(\mathrm{g}\right)+{\mathrm{SO}}_{3}\left(\mathrm{g}\right)$
Fe2O3 is reddish brown in color.

Hence, the correct answer is option 2.

#### Question 29:

A student took four test-tubes containing solutions of different colours marked I, II, III and IV as shown here. The test-tubes containing copper sulphate solution and ferrous sulphate solution could be the tubes :

(1) I and III
(2) II and III
(3) III and IV
(4) II and IV

The copper sulphate solution is of blue colour while the iron sulphate is of pale green colour.

Hence, the correct answer is option 4.

#### Question 30:

A student while heating solid lead nitrate taken in a test-tube would observe :
(1) white residue of PbO2
(2) green residue of NO2
(3) yellow residue of PbO
(4) brown residue of NO

When lead nitrate is heated, a yellow residue of lead oxide is obtained, and brown colored gas is liberated, i.e. nitrogen dioxide.
$2\mathrm{Pb}\left({\mathrm{NO}}_{3}{\right)}_{2}\to 2\mathrm{PbO}+4{\mathrm{NO}}_{2}+{\mathrm{O}}_{2}$

Hence, the correct answer is option 3.

#### Question 31:

Four students added a small amount of ethanoic acid to sodium hydrogencarbonate. The gas evolved was tested for its behaviour with burning splinter and lime water. They reported their observations as given below.

 Student Gas evolved Action on burning splinter Action on lime water A CO2 The flame of splinter extinguishes and gas does not burn Turned milky B SO2 The splinter burns brightly and the gas burns with a pop Turned green C NO2 The gas does not burn but the splinter burns with a hissing sound Turned black D O2 The gas burns with a yellow flame and the splinter extinguishes Turned purple
The correct observations have been reported by student:
(1) A
(2) B
(3) C
(4) D

When ethanoic acid is treated with sodium hydrogen carbonate, it will give sodium carboxylate salt, carbon dioxide, and water. Evolved carbon dioxide forms carbonate products which turns lime water milky.
${\mathrm{CH}}_{3}\mathrm{COOH}\left(\mathrm{aq}\right)+{\mathrm{NaHCO}}_{3}\left(\mathrm{s}\right)\to {\mathrm{CH}}_{3}\mathrm{COONa}\left(\mathrm{s}\right)+{\mathrm{CO}}_{2}\left(\mathrm{g}\right)+{\mathrm{H}}_{2}\mathrm{O}\left(\mathrm{l}\right)$

Hence, the correct answer is option 1.

#### Question 32:

A student was given an unknown solution in a test-tube. When he added universal indicator to the test-tube, the solution turned violet. The unknown solution is most likely to be :
(1) baking soda solution
(2) washing soda solution
(3) caustic soda solution
(4) household ammonia solution

A universal indicator takes the color of the solution to the blue-violet region if it is a base. As universal indicator turns the color of the given solution to violet, that's why the given solution is a baseOut of the given options, caustic soda is the strongest base and will violet color with universal indicator.

Hence, the correct answer is option 3.

#### Question 33:

A student placed a few drops of a liquid over a portion of the red litmus paper as shown here. He observed that the red litmus paper turned blue. The liquid could be :

(1) dilute hydrochloric acid
(2) dilute sodium hydroxide
(3) water
(4) dilute acetic acid

Bases turn blue litmus paper to red. Dilute sodium hydroxide convert red litmus to blue so; it is a base.

Hence the correct option is 2.

#### Question 34:

A student was asked to carry out a chemical reaction by placing four different metal strips in CuSOsolution for a considerable time, one by one. Which of the following metal strip will turn the blue CuSO4 solution to a colourless solution in due course of time?
(1) Fe
(2) Au
(3) Mg
(4) Ag

Out of all the given options, magnesium is most reactive so that it will displace the Cu from CuSO4 solution.
$\mathrm{Mg}\left(\mathrm{s}\right)+2{\mathrm{CuSO}}_{4}\left(\mathrm{aq}\right)\to \mathrm{Mg}\left({\mathrm{SO}}_{4}{\right)}_{2}+2\mathrm{Cu}\left(\mathrm{s}\right)$

Hence, the correct answer is option 3.

#### Question 35:

When a student added universal indicator solution to one of the following chemicals, its colour changed to navy blue. The chemical is most likely to be :
(1) lemon juice
(2) milk of magnesia
(3) vinegar
(4) tomato juice

A Base turns the red litmus to blue or any color in the blue-violet region depending upon the pH range of the base. Milk of magnesia or magnesium hydroxide is a base, that's why it turns the red litmus to navy blue.

Hence, the correct answer is option 2.

#### Question 36:

A student prepared hydrogen chloride gas by treating sodium chloride with concentrated sulphuric acid in a test-tube. He held a strip of dry blue litmus paper in HCl gas coming out of the test-tube. The student observed that on coming in contact with HCl gas, the colour of blue litmus paper :
(1) turned yellow
(2) turned violet
(3) remained blue
(4) turned red

In acidic solution, colour blue litmus paper is changed to red. So, hydrochloric acid gas turns blue litmus to red.

Hence, the correct answer is option 4.

#### Question 37:

When a student added a few drops of barium chloride solution to sodium sulphate solution, he obtained a white precipitate instantly. Which of the following type of chemical reaction has been carried out by the student?
(1) combination
(2) double displacement
(3) displacement
(4) decomposition

When barium chloride reacts with sodium sulphate, a white precipitate of barium sulphate is observed. Following reaction is the example of double displacement.
${\mathrm{BaCl}}_{2}+{\mathrm{Na}}_{2}{\mathrm{SO}}_{4}\to 2\mathrm{NaCl}+{\mathrm{BaSO}}_{4}$

Hence the correct option is 2.

#### Question 38:

A student placed a pinch of solid sodium hydrogencarbonate on a strip of red litmus paper. He found that the colour of red litmus paper strip :
(1) turned green
(2) turned blue
(3) turned violet
(4) did not change

Solid sodium hydrogen carbonate does not change the colour of litmus paper, as only ionic dissociation of molecules changes the colour of litmus paper.

Hence, the correct answer is option 4.

#### Question 39:

A student placed a clean iron nail in blue coloured copper sulphate solution for a considerable time. He observes that :
(1) iron nail gets green coating
(2) iron nail gets brown coating
(3) iron nail gets no coating
(4) iron nail gets blue coating

When an iron nail is placed is copper sulfate it will displace Cu from the solution as iron is more reactive than copper.

$\underset{\left(\mathrm{grey}\right)}{\mathrm{Fe}\left(\mathrm{s}\right)}+\underset{\left(\mathrm{blue}\right)}{{\mathrm{CuSO}}_{4}\left(\mathrm{aq}\right)}\to \underset{\left(\mathrm{green}\right)}{{\mathrm{FeSO}}_{4}\left(\mathrm{aq}\right)}+\underset{\left(\mathrm{brown}\right)}{\mathrm{Cu}\left(\mathrm{s}\right)}\phantom{\rule{0ex}{0ex}}$

The copper metal produced in this reaction forms a brown layer on the iron strip.

Hence, the correct answer is option 2.

#### Question 40:

Four students A, B, C and D were studying the effect of the solutions of hydrochloric acid, sodium hydroxide, sodium chloride and pure water respectively on blue litmus solution. Which of the students observed the colour change of blue litmus solution to red?
(1) A
(2) B
(3) C
(4) D

As student A has the hydrochloric acid, so he would observe the colour change of blue litmus solution to the red"

Hence, the correct answer is option 1.

#### Question 41:

Which one of the following solutions having same concentration will have lowest pH value?
(1) hydrochloric acid
(2) lemon juice
(3) water
(4) sodium hydroxide

pH scale varies from 0-14. Acids have a pH less than 7 while bases have a pH more than 7. Hydrochloric acid is a strong acid, so as compared to other options, it will have the lowest pH.

Hence, the correct answer is option 1.

#### Question 42:

We can show that iron is more reactive than copper :
(1) by preparing copper sulphate solution and dipping the iron strip in it.
(2) by dipping both the strips in water for some time.
(3) by preparing iron sulphate solution and dipping copper strip in it.
(4) by heating both iron and copper strip.

When an iron strip is dipped into a blue solution of copper sulphate, it turns the colour of the solution from blue to green due to the formation of ferrous sulphate. It happens because iron displaces the copper from copper sulphate solution and forms iron sulphate. This shows that iron is more reactive than copper. The reaction involved is as follows:

$\mathrm{Fe}\left(\mathrm{s}\right)+{\mathrm{CuSO}}_{4}\left(\mathrm{aq}\right)\to {\mathrm{FeSO}}_{4}\left(\mathrm{aq}\right)+\mathrm{Cu}\left(\mathrm{s}\right)$

Hence, the correct answer is option 1.

#### Question 43:

The pH of a sample of hydrochloric acid is 2. The pH of this sample when diluted by adding some water will be :
(1) more than 7
(2) more than 2 but less than 7
(3) unchanged
(4) less than 2 but more than 0

Hydrochloric acid is a strong acid but on the addition of water, its hydrogen ion concentration decreases so its pH will change. pH will become more than 2 but less than 7.

Hence, the correct answer is option 2.

#### Question 44:

Observe the given figures and choose the correct option :

(1) pH of I is greater than pH of II and III
(2) pH of III is greater than pH of I and II
(3) pH of I, II and III is equal
(4) pH of II is greater than pH of I and III

pH range of acids is less than 7 while bases have pH range more than 7. Water has a pH of 7. Sodium hydroxide is a base, so it will have maximum pH among the three solutions and hydrochloric acid being an acid will have the lowest pH.

Hence, the correct answer is option 4.

#### Question 45:

When treated with dilute hydrochloric acid, which of the following gives a gas which does not turn lime water milky?
(1) sodium sulphate
(2) sodium carbonate
(3) copper metal
(4) zinc metal

When hydrochloric acid is treated with zinc metal then zinc chloride form and hydrogen gas evolve.
$\mathrm{Zn}\left(\mathrm{s}\right)+\mathrm{HCl}\left(\mathrm{g}\right)\to {\mathrm{ZnCl}}_{2}\left(\mathrm{s}\right)+{\mathrm{H}}_{2}\left(\mathrm{g}\right)$
Hydrogen gas doesn't turn lime water milky, as there is no carbonate formation in the solution.

Hence, the correct answer is option 4.

#### Question 46:

Which one of the following procedures is correct to detect the acidic nature of SO2 gas?
(1) Insert wet blue litmus paper in a gas jar filled with SOgas
(2) Insert wet red litmus paper in a gas jar filled with SO2 gas
(3) Insert dry blue litmus paper in a gas jar filled with SOgas
(4) Insert dry red litmus paper in the gas jar filled with SO2 gas

To detect the acidic nature of sulphur dioxide, we will place a wet blue litmus paper inside the gas jar. So, that wet litmus paper traps the gaseous SO2 and converts the blue litmus to red.
We use wet litmus paper because when gas comes out, it can tested for acidity when they react with water in the litmus paper and form ions.

Hence, the correct answer is option 1.

#### Question 47:

Which of the following metal strips when placed in colourless AgNO3 solution, turns the solution blue?
(1) Fe
(2) Cu
(3) Mg
(4) Zn

Copper is more reactive than silver, it displaces silver from silver nitrate solution and forms blue coloured solution of copper nitrate.

Hence, the correct answer is option 2.

#### Question 48:

A small piece of aluminium metal was placed in a beaker containing a greenish solution. After some time, a grey coating was observed on the aluminium piece. The greenish solution is most likely to be :
(1) salt solution of copper metal
(2) salt solution of iron metal
(3) salt solution of zinc metal
(4) salt solution of aluminium metal

Aluminium is more reactive than all the metals given in the options. So, aluminium will displace metals from their respective salts.
From the given options we have salt of iron which is of greenish colour, when aluminium metal placed in iron salt solution colour of solution fades and aluminium piece gets grey coating.
$3{\mathrm{FeSO}}_{4}\left(\mathrm{aq}\right)+2\mathrm{Al}\left(\mathrm{s}\right)\to {\mathrm{Al}}_{2}\left({\mathrm{SO}}_{4}{\right)}_{3}\left(\mathrm{aq}\right)+3\mathrm{Fe}\left(\mathrm{s}\right)$

Hence, the correct answer is option 2.

#### Question 49:

A student measured the pH values of four solutions marked A, B, C and D and found them to be 6, 12, 2 and 14 respectively. The solution which is likely to be strongly acidic is :
(1) A
(2) B
(3) C
(4) D

Lower the value of pH stronger will be the acid. So, solution C will be the strongest acid.

Hence, the correct answer is option 3.

#### Question 50:

Which of the following solutions should be put on a universal indicator paper so that its colour may change to green?
(1) Milk
(2) Common salt solution
(3) Baking soda solution
(4) Milk of magnesia

The green colour of pH is shown by neutral molecules, so among the following options, common salt will show green colour.
Sodium chloride salt is formed from a strong acid hydrochloric acid and a strong base sodium hydroxide. Therefore, the aqueous solution of sodium chloride is neutral.

Hence, the correct answer is option 2.

#### Question 51:

A student took solution X in a test-tube and added a few drops of universal indicator to it. The solution turned blue. On adding another solution Y to this test-tube drop-wise, the colour of solution changed to green. When a yet another solution Z was added, the solution turned yellow. Which of the following gives the correct conclusion of the student?
(1) X is acid, Y is base, Z is salt solution
(2) X is base, Y is acid, Z is acid
(3) X is acid, Y is base, Z is base
(4) X is base, Y is acid, Z is sugar solution

Acids show blue colour with universal indicator, bases show red colour with universal indicator and neutral solution shows a green colour with the universal indicator. So from the given options X is a base as it shows blue colour, Y is a weak acid it shows green colour and Z shows yellow colour so it is also a weak acid.

Hence, the correct answer is option 2.

#### Question 52:

In order to study the neutralisation reaction of acid and base, a student took 10 mL of dilute hydrochloric acid in a conical flask and added a few drops of phenolphthalein indicator to it. He then added dilute sodium hydroxide solution to the conical flask dropwise with a dropper while shaking the conical flask constantly. When the acid is completely neutralised by the base, the solution in conical flask will turn :
(1) slightly red
(2) slightly yellow
(3) colourless
(4) slightly pink

Phenolphthalein is a colourless indicator in acid and in neutral solutions but in basic solutions, it shows pink color. So, when dilute sodium hydroxide is added until the acid is completely neutralized, the solution becomes colourless.

Hence, the correct answer is option 4.

#### Question 53:

In an experiment to measure the pH values of solutions, a student placed strips of universal indicator paper in four beakers containing solutions A, B, C and D. The colour of universal indicator paper in these solutions is as shown below :

The solution having lowest pH value is:
(1) A
(2) B
(3) C
(4) D

The universal indicator shows a wide range of colour differences in acids, bases, and neutral solutions. For strong acids, it shows a red colour, for moderate acids it changes from orange to yellow. Bases change from blue to indigo. On the pH scale, acids have the lowest value. So, solution C has the lowest pH as it is the strongest acid out of the given options.

Hence, the correct answer is option 3.

#### Question 54:

A student was given two metal strips X and Y alongwith colourless silver nitrate solution to perform two separate displacement reactions. When the student placed metal strip X in silver nitrate solution for a considerable time, he observed that the solution turned blue and a coating of silver metal was formed on the strip. And when the student immersed metal strip Y in silver nitrate solution for an equal time, he observed that the solution turned light green with the formation of a coating of silver metal on the strip. The correct conclusion of the student about the identity of metals X and Y is :
(1) X is copper and Y is magnesium
(2) X is zinc and Y is copper
(3) X is iron and Y is copper
(4) X is copper and Y is iron

For X, when silver nitrate is treated with X it gives the blue colour solution which means that that solution may contain copper. Copper is more reactive than silver, it will displace silver from the silver nitrate and form blue colour compound copper nitrate.
$\mathrm{Cu}\left(\mathrm{s}\right)+2{\mathrm{AgNO}}_{3}\left(\mathrm{aq}\right)\to \mathrm{Cu}\left({\mathrm{NO}}_{3}{\right)}_{2}\left(\mathrm{aq}\right)+2\mathrm{Ag}\left(\mathrm{s}\right)$

For Y, when silver nitrate is treated with Y it gives the light green colour solution which means that that solution may contain iron. Iron is more reactive than silver, it will displace silver from the silver nitrate and form green colour compound iron nitrate.

Hence, the correct answer is option 4.

#### Question 55:

A student was given four unknown solutions in test-tubes marked A, B, C and D and asked to test them with universal indicator solution. He observed that on putting universal indicator solution, the solutions A, B, C and D turned blue, orange, green and red respectively. The test-tube which contains sodium chloride solution is :
(1) A
(2) B
(3) C
(4) D

Formation of NaCl is an example of a neutralization reaction. It is formed by the reaction of strong acid and strong base. It has a neutral nature, so it shows a green colour with a universal indicator.

Hence, the correct answer is option 3.

#### Question 56:

When a student added red litmus to an aqueous solution, the red litmus turned blue. Which one of the following should be added in excess so that the change in colour is reversed?
(1) baking soda solution
(2) lime water
(3) vinegar solution
(4) ammonia solution

Acids turn blue litmus to red and bases turn red litmus to blue. When the student added red litmus to an aqueous solution, it turned blue which means, the solution is basic. To reverse the change in colour, now he has to add an acid to the solution in excess. So, from the given options only vinegar solution is acidic in nature. It is made up of ethanoic acid. When it will be added in excess in the solution, the solution will become acidic and the colour of the blue litmus then it can be changed back to red.

Hence, the correct answer is option 3.

#### Question 57:

A student was asked to test an unknown colourless solution with an indicator. When he added a few drops of phenophthalein indicator, the solution turned pink. Which one of the following chemicals should be added in excess so as to obtain the colourless solution again?
(1) HCI solution
(2) NaOH solution
(3) NH3 solution
(4) NaCI solution

Phenolphthalein is a universal indicator, it is colorless in an acidic and neutral environment but shows pink color in a basic environment.
As it shows a pink color, the solution is basic. Therefore, to obtain a colorless solution again, the student needs to add an excess of the acidic solution in it. So, out of all the given options, only the HCl solution is suitable.

Hence, the correct answer is option 1.

#### Question 58:

A student mixed equal volumes of hydrochloric acid and sodium hydroxide solution of same concentrations in a beaker and tested the pH of the resulting mixture with a pH paper. What will be the colour of pH paper in this case ?
(1) red
(2) yellow
(3) green
(4) blue

Hydrochloric acid is a strong acid and sodium hydroxide is a strong base, the reaction of strong acid and strong base is known as neutralization reaction. When strong acid and strong base reacts concentration of H+ and OH- ion becomes equal, they completely neutralize each other. So, the colour of the pH paper will be green.
$\mathrm{HCl}\left(\mathrm{aq}\right)+\mathrm{NaOH}\left(\mathrm{aq}\right)\to \mathrm{NaCl}\left(\mathrm{s}\right)+{\mathrm{H}}_{2}\mathrm{O}\left(\mathrm{l}\right)$

Hence, the correct answer is option 3.

#### Question 59:

In an experiment to measure the pH values by using a universal indicator, a student found that the pH values of four given solutions A, B, C and D are 10, 6, 2 and 14 respectively. The solution which will require the maximum volume of sodium hydroxide solution for complete neutralisation is solution :
(1) A
(2) B
(3) C
(4) D

When an acid reacts with a base and forms salt and water it is known as a neutralization reaction. Stronger the acid stronger the base required to neutralize it. So, the maximum amount of sodium hydroxide is required in "C" solution as it is the strongest acid among the following options.

Hence, the correct answer is option 3.

#### Question 60:

A student measured the pH values of four solutions P, Q, R and S as 10, 6, 0 and 12 respectively. The solution which is the most acidic is likely to be the solution :
(1) P
(2) Q
(3) R
(4) S

pH scale ranges from 0-14, acids have 0-6.9 range, bases have 7.1-14 and pH = 7 is neutral. Lower the value of pH stronger will be the acid, so solution having pH = 0 is the strongest acid, so R is the strongest acid.

Hence, the correct answer is option 3.

#### Question 61:

A student mixed some soil with water in a beaker and allowed it to settle. He filtered the contents of the beaker and obtained a clear filtrate. When he put a few drops of the filtrate on the pH paper, the pH paper turned yellowish orange. Which of the following should the student put on this pH paper so that it may change its colour to greenish-blue?
(1) NaHCO3 solution
(2) HCI solution
(3) Vinegar solution
(4) Common salt solution

The yellowish orange colour of the pH paper indicates it is an acid. So, to covert it to greenish blue we have to add a base in it. From the given options, sodium bicarbonate is a base which will again convert the colour of pH paper to greenish blue.

Hence, the correct answer is option 1.

#### Question 62:

When a student added a few drops of methyl orange indicator to a colourless solution, the solution turned red. Which of the following should he add in excess so that the colour changes to yellow ?
(1) NaOH solution
(2) H2SO4 solution
(3) Lemon juice
(4) Vinegar solution

Methyl orange turns red in the acidic solution and to convert it to the yellow colour, student needs to add excess of basic solution because in basic solution methyl orange shows yellow colour. So, out of given options, sodium hydroxide is a strong base which can change the colour of solution to yellow.

Hence, the correct answer is option 1.

#### Question 63:

A student measured the pH values of four solutions A, B, C and D which were found to be 4, 1, 13 and 11 respectively. Which of the following statements are correct about these solutions ?
(a) A is strong acid and B is weak acid
(b) B is strong acid and D is weak base
(c) D is strong base and C is weak base
(d) C is strong base and A is weak acid

(1) (a) and (b)
(2) (b) and (c)
(3) (c) and (d)
(4) (b) and (d)

pH scale ranges from 0-14. Acids have a range of 0-6.9 and bases have a range of 7.1-14. Lower the value of pH stronger the acid or higher the value of pH stronger will be the base. So, A and B are acids but pH of B is less than pH of A, so B is a stronger acid than A. C and D are the bases but pH of C is more than D, so C is stronger base than D.

Hence, the correct answer is option 4.

#### Question 64:

When a student put some copper turnings in a colourless solution, he observed that the solution gradually turned blue. The solution is most likely to be :
(1) ferrous sulphate solution
(2) magnesium nitrate solution
(3) silver nitrate solution
(4) copper sulphate solution

The silver nitrate solution is colourless in nature. When copper reacts with silver nitrate, it displaces silver from silver nitrate and forms copper nitrate solution, which is of blue colour.

Hence, the correct answer is option 3.

#### Question 65:

A student added blue litmus solution to a colourless aqueous solution. The solution turned red. Which one of the following chemicals should be added in excess so that the change in colour is reversed ?
(1) ethanol solution
(2) caustic soda solution
(3) hydrochloric acid solution
(4) vinegar solution

Acids turn blue litmus solution to red while bases turn red litmus solution to blue. When student added blue litmus solution to a colourless aqueous solution, the colour of litmus solution changed from blue to red, it means it was an acid. To reverse this process, a base should be added in excess in the solution. Bases change red litmus solution to blue and out of given options, caustic soda(chemically known as NaOH) is a strong base which can convert red litmus solution to blue.

Hence, the correct answer is option 2.

#### Question 66:

Aluminium sulphate and copper sulphate solutions were taken in two test tubes I and II respectively. Iron filings were then added to both the solutions. The four students A, B, C and D recorded their observations in the form of a table as given below.

 Student Aluminium sulphate solution (I) Copper sulphate solution (II) A Colourless changes to light green Blue colour of the solution is retained B Colour of colourless solution does not change Blue colour of the solution changes to light green C Colourless solution changes to light blue Blue colour of the solution changes to colourless D Colour of colourless solution remains unchanged Blue colour of the solution fades away
The correct set of observations have been recorded by the students :
(1) A
(2) B
(3) C
(4) D

In test tube I, an iron filling is added in a solution containing aluminium sulphate solution, no colour change will be observed as iron is not much reactive than aluminium, so it cannot displace aluminium from aluminium sulphate. So, no reaction takes place.
In test tube II, an iron filling is added in a solution containing copper sulphate solution, blue colour changes to light green. As iron is more reactive than copper, so it can displace aluminium from aluminium sulphate.

$3\mathrm{Fe}\left(\mathrm{s}\right)+{\mathrm{Al}}_{2}\left({\mathrm{SO}}_{4}{\right)}_{3}\left(\mathrm{aq}\right)\to 3{\mathrm{FeSO}}_{4}\left(\mathrm{aq}\right)+2\mathrm{Al}\left(\mathrm{s}\right)$

Therefore, the observations made by student "B" are correct.

Hence, the correct answer is option 2.

#### Question 67:

A student was given three solution marked X, Y, and Z, and asked to arrange them in the increasing order of their pH values. The student put two drops of each solution on three strips of universal indicator paper separately. The colours shown by the three indicator strips are as follows:

Which of the following gives the correct increasing order of pH values ?
(1) Z < X < Y
(2) Y < Z < X
(3) X < Y < Z
​(4) Z < Y < X

A universal indicator shows red to yellow colour for acids, and blue to indigo shows base. So, when a student puts drops of X with universal indicator gives blue colour, so it is a base, Y with universal indicator gives yellow colour, so it is an acid, Z with universal indicator gives the green colour, so it is neutral. So, by the variation in the colour of pH paper, we can arrange them in increasing order: Y < Z < X.

Hence, the correct answer is option 2.

#### Question 68:

When the strip of pH paper was put in a given solution, the pH paper changed to orange red. The given solution is most likely to be of :
(1) sodium hydroxide
(2) hydrochloric acid
(3) sodium bicarbonate
(4) ethanoic acid

Acids turn blue litmus to red. So, among the given options, hydrochloric acid and acetic acid are two acids. But hydrochloric acid is a strong acid it will give red colour on pH paper and acetic acid is a weak acid it gives orange-red colour on pH paper.

Hence, the correct answer is option 4.

#### Question 69:

The test-tube I contains sodium bicarbonate soultion whereas test-tube II contains lemon juice. On introducing pH paper strips in both the solutions, it is observed that the pH paper turns :
(1) red in I and blue in II
(2) blue in both
(3) blue in I and red in II
(4) red in I and pink in II

Sodium bicarbonate is a base it turns red litmus to blue, Lemon juice (chemically it is citric acid) is an acid it turns blue litmus to red.

Hence, the correct answer is option 3.

#### Question 70:

No observable change is noticed when dilute hydrochoric acid is added to :
(1) sodium hydroxide solution
(2) sodium carbonate solution
(3) blue litmus solution
(4) zinc metal

When dilute hydrochloric acid is treated with sodium hydroxide, it forms a salt and water. Neither colour change nor the precipiate formation is observed during this reaction.
$\mathrm{HCl}\left(\mathrm{aq}\right)+\mathrm{NaOH}\left(\mathrm{aq}\right)\to \mathrm{NaCl}\left(\mathrm{aq}\right)+{\mathrm{H}}_{2}\mathrm{O}\left(\mathrm{l}\right)$

Hence, the correct answer is option 1.

#### Question 71:

A student took four test-tubes I, II, III and IV containing aluminium sulphate, copper sulphate, ferrous sulphate and zinc sulphate solutions respectively. He placed iron strips in each one of them. After some time, he found a brown deposit formed in test-tube marked :

(1) I
(2) II
(3) III
(4) IV

In test tube II, iron is more reactive than copper, so it will displace copper from the copper sulphate solution. Due to this displacement reaction colour of solution changes from blue to green. The iron nail gets brown colour due to deposition of copper metal on its surface.
$\underset{\left(\mathrm{Grey}\right)}{\mathrm{Fe}}\left(\mathrm{s}\right)+\underset{\left(\mathrm{Blue}\right)}{{\mathrm{CuSO}}_{4}}\left(\mathrm{aq}\right)\to \underset{\left(\mathrm{Green}\right)}{{\mathrm{FeSO}}_{4}}\left(\mathrm{aq}\right)+\underset{\left(\mathrm{Brown}\right)}{\mathrm{Cu}}\left(\mathrm{s}\right)$

Hence, the correct answer is option 2.

#### Question 72:

2 mL of ethanoic acid was taken in each of test-tube I and test-tube II. A red litmus paper was introduced in test-tube I and a pH paper was introduced in test-tube II. The experiment was performed by four students A, B, C and D, they reported their observations as given below :

 Student Action on red litmus Action of pH paper A B C D Turned blue Remains unchanged  Turned blue Remains unchanged Turned pink Turned green Turned blue Turned pink
The correct set of observations was made by the student :
(1) A
(2) B
(3) C
(4) D

As ethanoic acid is an acid, it will convert blue litmus to red. So, observation of student D on the action of litmus is correct as red litmus remain unchanged and pH paper will turn pink(because it is a weak acid).

Hence, the correct answer is option 4.

#### Question 73:

Four students A, B, C and D were asked by their teacher to arrange the set-ups I to IV as given below and identify the gas, if any, evolved in each case :

After observation, the students arrived at the inferences recorded in the following table :

 Students I I III IV A B C D Hydrogen Carbon dioxide Carbon dioxide No gas No gas Hydrogen  Hydrogen Carbon dioxide Carbon dioxide No gas  Hydrogen Carbon dioxide Hydrogen Carbon dioxide No gas Hydrogen
The correct observations and inferences have been reported by the student :
(1) A
(2) B
(3) C
(4) D

In the setup I, sodium carbonate treated with dilute hydrochloric acid, it gives carbon dioxide and sodium chloride.
${\mathrm{Na}}_{2}{\mathrm{CO}}_{3}\left(\mathrm{aq}\right)+2\mathrm{HCl}\left(\mathrm{aq}\right)⇋2\mathrm{NaCl}\left(\mathrm{aq}\right)+{\mathrm{H}}_{2}\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{CO}}_{2}\left(\mathrm{g}\right)$
In setup II, when sodium hydroxide is treated with zinc, it gives zinc chloride and hydrogen gas will evolve.
$\mathrm{NaOH}\left(\mathrm{aq}\right)+\mathrm{Zn}\left(\mathrm{s}\right)\to {\mathrm{Na}}_{2}{\mathrm{ZnO}}_{2}\left(\mathrm{aq}\right)+{\mathrm{H}}_{2}\left(\mathrm{g}\right)$
In setup III, when dilute hydrochloric acid reacts with zinc, it will give zinc chloride and hydrogen gas will evolve.
$\mathrm{Zn}\left(\mathrm{s}\right)+\mathrm{HCl}\left(\mathrm{aq}\right)\to {\mathrm{ZnCl}}_{2}\left(\mathrm{aq}\right)+{\mathrm{H}}_{2}\left(\mathrm{aq}\right)$
In setup IV, when sodium carbonate reacted with sodium hydroxide, no reaction takes place.

So, observations made by student C are correct.

Hence, the correct answer is option 3.

#### Question 74:

On adding a few drops of universal indicator solution to three unknown colourless solutions P, Q, and R taken separately in three test-tubes shown in the diagrams, a student observed the changes in colour as green in solution P, red solution Q and violet in solution R.

The decreasing order of the pH of the three solution is :
(1) P > Q > R
(2) R > P > Q
(3) Q > P > R
(4) R > Q > P

The universal indicator shows a wide range of colour difference for acids and bases. Acids show red to yellow colour, bases show blue to indigo, and neutral molecules show green colour. P shows green colour, so it is neutral, Q shows red colour, so it is an acid and R shows violet colour, so it is a base.
So, from the above discussion, we can arrange the given molecules in decreasing order: R > P > Q.

Hence, the correct answer is option 2.

#### Question 75:

A few drops of ethanoic acid were added to solid sodium carbonate. The observation made was that :
(1) a hissing sound was produced
(2) brown fumes evolved
(3) brisk effervescence occurred
(4) a pungent smelling gas was evolved

$2{\mathrm{CH}}_{3}\mathrm{COOH}\left(\mathrm{aq}\right)+{\mathrm{Na}}_{2}{\mathrm{CO}}_{3}\left(\mathrm{s}\right)\to 2{\mathrm{CH}}_{3}\mathrm{COONa}\left(\mathrm{aq}\right)+{\mathrm{CO}}_{2}\left(\mathrm{g}\right)+{\mathrm{H}}_{2}\mathrm{O}\left(\mathrm{l}\right)$