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Page No 369:

Question 1:

Why are iron grills painted frequently?


Iron objects when they are in contact with air and moisture they are prone to rust. Thus, to prevent the rusting of iron, iron objects are painted as the upper layer gets protected from air and moisture.

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Question 2:

Out of plane mirror, convex mirror and concave mirror:
(a) Which mirror is used as a reflector in the headlights of a car?
(b) Which mirror is used as a rear-view mirror in a car?


(a) The concave mirrors are used in the headlights of a car to get powerful beams of light. 

(b) Convex mirrors are used as rear view mirror of a car because convex mirrors always form an erect and diminished image. Which helps the driver to see a wider view.

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Question 3:

An element X is in group 13 of the periodic table.
(a) What will be the formula of its chloride?
(b) What will be the formula of its oxide?


Valence shell of element X contains three electrons.

(a) The formula of chloride of element X will be XCl3.

(b) The formula of an oxide of element X will be X2O3.

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Question 4:

The focal length of a concave lens is 20 cm. If an object is placed at a distance of 50 cm in front of this concave lens, where is the image formed? What is the nature of the image?


Focal length of concave lens = 20 cm

Object distance = 50 cm

Using lens formula, 1v-1u=1f

1v=1-20+1-50=-7100v=-1007 cm

The image formed is virtual, erect and diminished in size.

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Question 5:

State two advantages of constructing large dams on rivers for the generation of electricity. Also mention two problems associated with these dams.


Advantages of constructing large dams -

  • The water stored in dams is used for irrigation throughout the year, irrespective of the season. For example, the Indira Gandhi Canal originates in Bhakra dam and provides water to several areas in Rajasthan.
  • Dams are also equipped with turbines and generators to produce hydroelectricity.
Disadvantages of constructing large dams -

• The destruction of huge areas of forests.
• The destruction of forests leads to the loss of floral and fauna species that are indigenous to the particular area.

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Question 6:

The electronic configurations of four elements A, B, C and D are as follows:

A 2, 8, 1
B 2, 8, 7
C 2, 8, 8
D 2, 4
(a) Which of these elements is a metal?
(b) Which of these elements are non-metals?
(c) Which two elements will combine to form an ionic bond?
(d) Which two elements will combine to form a covalent bond?
(e) Which element will form an anion of valency 1?
(f) Which element is a noble gas?


(a) Element A is metal, as it belongs to the alkali metal group(1) of the modern periodic table.

(b) Element D is a non-metal, as it belongs to the carbon family(14) of the modern periodic table.

(c) An ionic bond is formed by permanent transfer of electrons, so element "A" will lose one electron to achieve noble gas configuration and element "B" will gain an electron to achieve the noble gas configuration. So, ionic bond forms between A and B.

(d) The covalent bond is formed by sharing of electrons, so element "B" requires an electron to achieve the noble gas configuration and "D" requires four electrons to achieve the noble gas configuration. Hence,  D will form four single bonds with four molecules of B.

(e) Element "B" will form an anion of valency 1, as it will accept one electron from other donating species.

(f) Element "C" is a noble gas element, as its outer most shell is fully filled.

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Question 7:

Which gas is liberated when dilute hydrochloric acid reacts with zinc metal? Write a balanced chemical equation for the reaction which takes place. How will you test this gas? Name a metal which produces the same gas just by reacting with cold water.


When dilute hydrochloric acid reacts with zinc metal, zinc will displace hydrogen from hydrochloric acid and form zinc chloride. It is accompanied by the release of hydrogen gas.


When we place a burning candle near the mouth of the test tube a pop-up sound is produced which confirms the presence of hydrogen gas in solution.
Sodium metal on reaction with cold water gives sodium hydroxide and hydrogen gas will evolve.


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Question 8:

The following diagram shows a part of the periodic table in which the elements are arranged according to their atomic numbers. (The letters given here are not the chemical symbols of the elements):

(i) Which element has a bigger atom, a or f?
(ii) Which element has a higher valency, k or o?
(iii) Which element is more metallic, i or k?
(iv) Which element is more non-metallic, d or g?
(v) Select a letter which represents a non-metal of valency 2.
(vi) Select a letter which represents a noble gas.


(a) As we move from left to right in a periodic table size of element decreases due to the increase in the number of electrons in the shell, they are pulled strongly towards the nucleus. Hence, the bigger atom is "a".

(b) Valency can be defined as the number of electrons available for bond formation.
Valency of k = 3
Valency of o = 1
Hence, "k" have higher valency. 

(c) On movind left to right in a periodic table metallic character decreases.
On moving down the group metallic character increases.
So, "i" will be more metallic.

(d) On moving left to right in a periodic table non-metallic character increases.
On moving down the group non-metallic character decreases
So, "g" will be more metallic.

(e) Valency can be defined as the number of electrons available for bond formation.
Valency of f and n is 2.

(f) "h" and "p" represents noble gas.

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Question 9:

You are given three test-tubes which contain an acidic solution, a basic solution and distilled water, separately. If you are provided only red litmus paper, how will you identify the contents of each test-tube?


We seperately dip red litmus paper in three solutions, the basic solution will turn red litmus to blue. After that we use that blue litmus in other two solutions to test acidic solution, when we dip blue litmus in two solutions acidic solution will turn blue litmus to red and the remaining solution will be distilled water.

Page No 370:

Question 10:

(a) For which position of an object, a concave mirror forms a real image equal in size to the object?
(b) State one use of a concave mirror.
(c) An object of height 1 cm is placed at a distance of 15 cm from a concave mirror of radius of curvature 20 cm. Find the position, nature and size of the image formed.


(a) When the object is placed at the radius of curvature of a concave mirror, then the image formed is equal in size with the object. 

(b) Concave mirrors are used in motor vehicle headlights to reflect strong beams of light.

(c) Radius of curvature of the lens = 20 cm

Focal length = 10 cm

Object distance = 15 cm

Using mirror formula, 1v+1u=1f

1v=1-10-1-15=-130v = 30 cm

Magnification of the mirror is given by the relation,

 m = -vu=-3015=-2m=-2=hihohi=-2ho=-2×1 cm = -2 cmhi=-2 cm

Nature of the image is virtual, inverted and enlarged.

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Question 11:

The position of the hand shown in the figure corresponds to one of Fleming's rules.

(a) Which Fleming's rule is illustrated by this hand?
(b) In this figure of hand, what is indicated:
     (i) by the direction of forefinger?
     (ii) by the direction of thumb?
     (iii) by the direction of center finger?


(a) Fleming's right-hand rule is illustrated in the figure. 

(b) (i) The motion of the conductor.
(ii) Magnetic field
(iii) Current

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Question 12:

(a) An object is placed between f and 2f in front of a convex lens. Draw a labelled ray-diagram to show the formation of image.
(b) State whether the image formed is real or virtual.
​(c) State whether the image formed is diminished or enlarged.




(b) The image formed is real.

(c) The image formed is enlarged.

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Question 13:

Draw a labelled diagram of the human digestive system.
(a) In which part of the digestive system is water absorbed?
​(b) Where is digested food absorbed in the human body?


Human digestive system

(a) Water is absorbed in the large intestine.
(b) Food is absorbed in the small intestine.

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Question 14:

Which acid is produced in our stomach? What happens if there is an excess of acid in the stomach? How can its effect be cured?


Hydrochloric acid is produced in the stomach. Production of too much of acid in the stomach leads to the irritation of the stomach lining. This in turn can lead to formation of ulcers in the stomach. Excess acid can be neutralised by taking antacids which are basic in nature.

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Question 15:

Explain the term rancidity. Write any two methods to prevent (or retard) the development of rancidity in fat and oil containing foods. Name another damaging effect caused by the same natural process which produces rancidity.


Fats and oils when kept for a long time get oxidized because of which the taste and odour of food containing these fats changes and it becomes unfit for consumption. This is called rancidity.
Following ways can prevent rancidity:
i) Storing food in an airtight container.
ii) Antioxidants are added to foods containing fats and oils.
iii) Flushing packed food items with an inert gas like nitrogen.

When fatty substances are exposed to air, its unsaturated components are converted into hydroperoxides, which break down into volatile aldehydes, esters, alcohols, ketones, and hydrocarbons, some of which have disagreeable odours. 


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Question 16:

(a) When sodium is burnt in chlorine, sodium chloride is formed, and when molten sodium chloride is electrolysed, then sodium and chlorine are formed. What type of reaction takes place:
    (i) in the first case?
    (ii) in the second case?
(b) When hydrogen is passed over heated copper oxide, copper and steam are formed. Write a balanced chemical equation for this reaction. State which of the chemicals is oxidised and which one is reduced?
​(c) What would you observe when zinc is added to a solution of iron sulphate? Write the chemical equation of the reaction which takes place. Why does this reaction occur?


(i) When sodium is burnt in chlorine, due to addition reaction sodium chloride is formed.
(ii) When this sodium chloride is electrolyzed, sodium chloride is decomposed into its ionic state as sodium ions and chloride ions.
At cathode: NaNa++e-At anode:Cl+e-Cl-Net reaction: Na+ClNaCl 
So, it is a decomposition reaction.

(b) When hydrogen gas is passed over heated copper oxide, then the black copper oxide is reduced and red-brown copper metal is obtained. The reaction involved can be shown as:
As copper is losing oxygen and hydrogen is accepting oxygen, so copper is reduced and hydrogen is oxidized.

(c) When zinc is added to a solution of iron sulphate, then it would displace iron from the solution and form zinc sulphate.
This reaction is an example of a displacement reaction because zinc is more reactive than iron, zinc will displace iron from the solution.


Page No 371:

Question 17:

(a) Write the functional groups present in an aldehyde and a carboxylic acid.
(b) How would you distinguish between an alcohol and a carboxylic acid?
(c) What happens when ethanoic acid is warmed with ethanol in the presence of a few drops of concentrated sulphuric acid? Write equation of the reaction involved.
(d) What happens when a piece of sodium metal is added to ethanol? Write equation of the reaction which takes place.
​(e) Describe how ethene can be prepared from ethanol? Give an equation of the reaction and state the conditions.


(a) The functional group present in an aldehyde will be carbonyl group and in carboxylic acid will be carboxyl group.

(b) Ethanol and ethanoic acid can be distinguished by reaction with sodium hydroxide. Ethanol does not react with sodium hydroxide, but ethanoic acid reacts with sodium hydroxide to form sodium ethanoate and water.
Ethanol has a sweet and pleasant smell but ethanoic acid has a pungent odour.

(c) When ethanoic acid is warmed with ethanol in the presence of a few drops of concentrated sulphuric acid, we will get a sweet smelling ester ethyl ethanoate.

(d) When a piece of sodium metal is added to ethanol, sodium ethoxide is formed with the evolution of hydrogen gas.

(e) By acidic hydrolysis of ethanol, dehydration of ethanol will occur which lead to the formation of ethene.


Page No 371:

Question 18:

(a) What is meant by series and parallel combination of resistances?
(b) In which case, series combination or parallel combination, the combined resistance is less than any of the individual resistances?
(c) How should two resistances of 2 Ω each be connected so as to produce an equivalent resistance of 1 Ω?
In the circuit diagram given here, find:
(i) total resistance of the circuit,
(ii) total current flowing in the circuit, and
​(iii) the potential difference across R1


(a) In a series combination, resistances are connected by an end to end such that the current flowing through all of them is equal. Whereas in a parallel combination, the resistances are connected in such a manner that they get an equal voltage.

(b) In a parallel combination, the reciprocal of net resistance is equal to the sum of reciprocals of individual resistances. Hence, in a parallel combination of resistances, the net resistance is smaller than any of the individual resistances. 

(c)  Two resistances of 2 Ω each should be connected in parallel. The net resistance of the parallel combination of both the resistors would be equal to 1 Ω. 

1Rnet=1R1+1R2=12+12=1Rnet= 1 Ω


(i) As we can see in the figure, Resistances R2 and R3 are connected in parallel.

The net resistance of the parallel combination = R2R3R2+R3=8×128+12=9620=4.8 Ω

Now, the equivalent resistance of the whole circuit is the series combination of R1 and net resistance of parallel combination.

Equivalent resistance = 7.2 Ω +4.8 Ω =12 Ω

(ii) Current in the circuit = Total voltage appliedTotal resistance=6 V12 Ω=0.5 A

(iii) The potential difference across R1 = Current through R1 × Resistance of R1 = 0.5 A ×7.2 Ω=3.6 V

Page No 371:

Question 19:

(a) What is meant by the heating effect of current? State thee factors on which the heat produced in a wire by an electric current depends.
(b) Explain why, though the heating element of an electric heater glows but its connecting cord does not glow.
(c) An electric geyser of resistance 20 Ω takes a current of 5 A. Calculate the heat produced in 2 minutes.
​(d) Name the commercial unit of electric energy. How many joules are equal to this unit?


(a) When an electric current flows in a circuit, it produces heat across the resistive elements of the circuit. This is called the heating effect of current. The heat produced depends on the following factors:

(i) Current flowing the circuit.
(ii) The resistance of the circuit.

(b) The heating element of the heater is made up of an alloy which has very high resistance. So, when current flows through the heating element, it becomes too hot and glows red due to the heating effect of current. But, the resistance of cord which is usually of copper or aluminium is very low, so it does not glow.

(c) The heat produced in the geyser = I2Rt (Where 'I'  is current, 'R' is the resistance and 't' is the time for which the current flows)

In the given case, Resistance of the geyser = 20 Ω

Current flow = 5 A

Time of current flow = 2 minutes = 120 seconds

Heat produced = (5)2×20×120=60 KJ

(d) Commercial unit of electric energy is 'kWh'. 1 kWh = 3.6×106 J

Page No 371:

Question 20:

What are the various organs of the blood circulatory system in humans? Describe the circulation of blood in the human body with the help of a flowchart. Why is the blood circulatory system in humans called a "double circulation"?


The circulatory system consists of the following organs - four-chambered heart, a network of branching blood vessels and blood.
The blood vessels are of three types - veins, arteries and capillaries.


Double circulation is the process of passing blood twice through the heart in one cycle. It occurs in bigger organisms like mammals and birds requiring more metabolic energy.

The four-chambered heart in humans contains two auricles (left and right) and two ventricles (left and right). The left part of the heart contains oxygenated blood and the right part of the heart contains deoxygenated blood. Thus, blood passes two times in one complete circuit—one with oxygenated blood and the other with deoxygenated blood. This is double circulation. The double circulation system prevents the mixing of oxygenated and deoxygenated blood.


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Question 21:

(a) What is puberty? What changes are seen in boys and girls at the time of puberty?
​(b) Draw a neat, labelled diagram of the human male reproductive system and describe it briefly. Why are testes outside the abdominal cavity? What is the role of seminal vesicles and prostrate glands in the human male reproductive system?


(a) Puberty is the process in which the body attains sexual maturity by having well-developed sex organs, and becomes capable of reproduction.

Changes that occur in females during puberty:

(i) development of breasts

(ii) softening of voice

(iii) ovum begins to mature with the onset of puberty.

(iv) occurrence of the menstruation cycle (first menstrual flow beginning at puberty is called menarche, and the stoppage of menstruation at the age of 45 − 50 years is called menopause.)

Changes that occur in males during puberty:

  • Under the influence of hormones, the larynx develops prominently. The vocal cord become longer and thicker in boys, causing the voice to become hoarse.
  • Growth of hair in other areas of skin like underarms, face, hands, and legs.
  • Enlargement of the testicles followed by penis.
  • Testes grow and start producing sperms.


Testes - They are located outside the abdominal cavity within a pouch called the scrotum. The function of the testes is to produce sperms and a hormone called testosterone, which brings about secondary sex characteristics in boys.

Vas deferens - It carries the sperms from the testes to the urethra. It also receives the ducts, which bring products from the seminal vesicles and prostate glands.

Seminal vesicles and prostate glands - The fluids from these organs provide nutrients in the form of fructose, calcium, and some enzymes. The sperms produced in the testes are carried by the vas deferens. The secretions from the seminal vesicles and prostate glands lubricate the sperms.

Testes are located outside the abdominal cavity, within a pouch called the scrotum. For the production of sperms, testes require a temperature that is 2–2.5 °C lower than the temperature of the rest of the body. That is why testes are protected inside the scrotum. 

Role of seminal vesicles and prostate gland -

(i) Seminal vesicles - The secretions of seminal vesicles contain many proteins and enzymes and thus provide nutrition to the developing sperms.

(ii) Prostate gland - The prostate gland secretes a slightly alkaline fluid that lubricates the sperms and neutralises the acidity of the vaginal tract.

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Question 22:

While performing an experiment by using a given voltmeter, a student observes that the needle indicates 12 divisions on the voltmeter scale. If the voltmeter scale has 5 divisions between 0 and 1 V, then what is the value corresponding to 12 divisions?


5 divisions of voltmeter scale = 1 V

1 division of voltmeter scale = 0.2 V

Hence, 12 divisions of voltmeter scale = 2.4 V

Page No 372:

Question 23:

In an electric iron being used in a household, the plastic insulation of live wire and neutral wire in the connecting cable gets torn. Due to this, naked live wire touches the naked neutral wire directly and the electric fuse of the circuit blows off.
(a) What term is used to indicate the touching of naked live wire and neutral wire directly?
(b) When the naked wires touch each other directly, what happens to the resistance of the circuit so formed?
(c) What happens to the current flowing through the wires under these conditions?
​(d) Which wire connected to the body of an electric iron protects the person using this electric iron from electric shock?


(a) The touching of a naked live wire and a naked neutral wire is termed as short-circuiting.

(b)  When the naked wires touch each other directly, the resistance of the circuit becomes negligible. That's why, short-circuiting results in a high flow of current in the circuit, which sometimes damages the electrical components. 

(c) During short-circuiting, the resistance of the circuit becomes negligible. So, the current in the circuit becomes too high. 

(d) The earth wire protects the person from getting an electric shock.

Page No 372:

Question 24:

A student carries out the decomposition reaction of lead nitrate to form three simpler substances. One of the substances formed during this reaction is a brown coloured gas whereas another substance formed is a yellow coloured solid.
(a) What is the colour of lead nitrate?
(b) How is the decomposition reaction of lead nitrate carried out?
(c) Name the brown coloured gas produced in this reaction.
​(d) Name the yellow solid formed in this reaction.


(a) Lead nitrate is of white colour.

(b) When lead nitrate is heated, it is decomposed into three simpler products - yellow coloured lead oxide, brown fumes of nitrogen dioxide and oxygen.

Pb(NO3)2white(s)heatPbO(s)yellow+NO2(g)brown fumes+O2(g)

(c) Brown coloured gas is nitrogen dioxide.

(d) Yellow coloured solid formed is lead oxide.


Page No 372:

Question 25:

While working in a chemistry laboratory, a student took some zinc granules in a test-tube and added a liquid X to it. A gas Y was produced. When a burning matchstick was brought near the mouth of the test-tube, the gas Y burns with a 'pop' sound, making a little explosion.
(a) What could the liquid X be?
(b) Name the gas Y.
​(c) State two properties of gas Y.


(a) When student adds liquid X in zinc granules, a gas Y is produced with a pop sound, which means that gas Y will be hydrogen. 
So, liquid X must be a hydrogen-containing compound, it can be hydrochloric acid.


(b) Gas Y will be hydrogen.

(c) Properties of hydrogen gas:
(i) It easily reacts with oxygen to form water.
(ii) It is used as an energy medium in lot of combustion reactions.
(iii) It is used as rotor coolant in electrical generators.

Page No 372:

Question 26:

A student visits hill station in North India during the summer vacations. He observes that some of the people in that area have swollen  necks.
(a) Name the disease from which the people with swollen necks are suffering.
(b) What is the cause of this disease?
(c) Why is this disease more prevalent in hilly areas?
(d) What should be done to prevent this disease?


(a) These people must be suffering from goitre.
(b) This disease is caused due to deficiency of thyroxine hormone.
(c) The food grown in hilly areas is deficient of iodine because lot of iodine leaches out from the soil in this region. As a result of which, people suffer from goitre in hilly regions.
(d) This disease can easily be prevented by consuming iodised salt in their daily diet.

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Question 27:

In the experiment to show that sunlight is necessary for photosynthesis:
(a) What is done to destarch the green leaves of the potted plant initially?
(b) What is done to a part of destarched leaf so that photosynthesis may not take place in that part of the leaf (before keeping the potted plant in sunlight)?
(c) How is chlorophyll removed from the green leaf before further testing?
(d) Which reagent is used to test the presence/absence of starch in the parts of experimental leaf?


(a) Initially, the plant is kept in dark for 24 hours to destarch the leafs.
(b) A part of destarched leaf is covered with black paper so that the light does not reach that region and photosynthesis does not occur.
(c) The chlorophyll is removed from the leaf green leaf before testing by boiling it in alcohol.
(d) The reagent used to test the presence of starch is called iodine.

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