Lakhmir Singh Manjit Kaur Chemistry 2020 2021 Solutions for Class 9 Science Chapter 9 Model Test Paper 4 are provided here with simple step-by-step explanations. These solutions for Model Test Paper 4 are extremely popular among Class 9 students for Science Model Test Paper 4 Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Lakhmir Singh Manjit Kaur Chemistry 2020 2021 Book of Class 9 Science Chapter 9 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Lakhmir Singh Manjit Kaur Chemistry 2020 2021 Solutions. All Lakhmir Singh Manjit Kaur Chemistry 2020 2021 Solutions for class Class 9 Science are prepared by experts and are 100% accurate.

#### Question 1:

Fill in the blanks:
Cell theory was first given by ................ and ................. .

Cell theory was first given by Jakob Matthias Schledian and Theodor Schwann.

#### Question 2:

How many chambers are present in the heart of: (i) Fishes; (ii) Frog?

(i) Fishes have a two chambered heart.

(ii) Frogs have a three chambered heart.

#### Question 3:

Explain why, school bags are provided with wide straps to carry them.

School bags are provided with wide straps to reduce the pressure on our shoulders.

According to the relation, the pressure is indirectly proportional to the area exposed to the force. That's why if we increase the area exposed to the force by the bag on our shoulders, then we feel less pressure.

#### Question 4:

What are longitudinal waves and transverse waves? Explain with the help of labelled diagrams.

Longitudinal waves are those in which particles of the medium vibrate in the direction of propagation of the wave. Whereas, transverse waves are those in which particles of the medium vibrate perpendicularly to the direction of propagation of the wave. The following diagrams explain both types of waves:

#### Question 5:

Write one main function of (a) Apical meristem (b) Lateral meristem.

(a) Apical meristems are located at the apical regions of the plant and they help in the growth of the root and shoot tips.

(b) Lateral meristems are located beneath the cork cambium and help in increasing the width (secondary growth) of the plant.

#### Question 6:

Why is heat energy needed to melt a solid? What is this heat energy called?

Heat energy is needed to convert solid into a liquid because heat energy increases the kinetic energy of particles. As the kinetic energy increases, the movement of the particles increases and eventually the bond or attraction between the particles gets broken and the particles start moving faster. Moving faster cause the state of the matter to change because the particles in solid are rigid but when the heat is applied the particles are loosened and start moving freely. So, it changes into a liquid state.
The heat energy that it used to change 1 kg of solid into liquid at atmospheric pressure and its melting point is called the latent heat of fusion.

#### Question 7:

Differentiate between prokaryotic and eukaryotic cells.

The differences between prokaryotic and eukaroyotic cells are as follows:

 Prokaryotic cells Eukaryotic cells 1. These cells are generally small in size. 1. These cells have a comparatively larger size. 2. The nucleus is not enclosed by a nuclear membrane. 2. Nucleus is enclosed by a well-defined nuclear membrane. 3. Membrane bound organelles such as mitochondria and lysosomes are not present. 3. Membrane bound organelles are abundantly found in eukaryotic cells. 4. Genetic material is present in the form of nucleoid. 4. Genetic material is present within the nucleus. 5. Cell wall made up of peptidoglycans is present in certain prokaryotic bacteria. 5. Cell wall made up of cellulose is present in case of plants while animal cells lack cell wall.

#### Question 8:

An element Z forms an oxide ZO3.
(a) What is the valency of element Z?
(b) What will be the formula of fluoride of Z?

(a) Valency of Z = 6

(b) The formula for fluoride of Z is ZF6.

#### Question 9:

(a) What are isotopes? Explain by giving an example.
(b) Give one similarity and one difference between a pair of isotopes.

(a) Isotopes are defined as atoms having the same atomic number, but different mass numbers. These atoms contain an equal number of protons and electrons, but different number of neutrons.
For eg. In nature hydrogen is found in three forms with different mass numbers, namely .

(b) Similarity: Isotopes have similar atomic number
Difference: Isotopes have different mass number.

#### Question 10:

(a) Derive the formula: s = ut + 1/2 at2, where the symbols have usual meanings.

Let the initial velocity of a body is 'u' and the final velocity of the body is 'v'.

The average velocity of the body = $\frac{u+v}{2}$

If the body takes time 't' to travel a distance of 's', then,

$s=\frac{u+v}{2}×t$  .......(1)

Using the first equation of motion we can write, u +at  .......(2) (Where 'a' is the acceleration of the body)

Putting the value of 'v' from equation (2) into equation (1), we get,

#### Question 11:

Discuss the conservation of momentum in each of the following cases:
(i) a rocket taking off from ground.
(ii) flying of a jet aeroplane.

(i) When a rocket takes off, hot burning gases eject at very high pressure and speed in a downward direction. As the linear momentum of the gases and the rocket is conserved before ejaculation of the gases. Hence, to keep the momentum conserved after the ejection of high-speed gases, an upward thrust works on the rocket which takes it upward with high acceleration. That's how a rocket takes off of the ground.

(ii) In a Jet aeroplane, the rate of burning of the fuel and the rate of ejection of exhaust gases is kept in such a way, that it provides the right amount of forwarding push which helps the jet to gain the desired change in momentum and accelerate accordingly.

So, the conservation of momentum is also applicable here. Ejection of exhaust gases at high speed in the backward direction disturbs the linear momentum of the jet. Hence, a forward thrust acts on the jet which accelerates it in such a way that it suffers an equal change in momentum in forwarding direction. That's how a jet aeroplane flies at high speeds.

#### Question 12:

Define the terms 'frequency', 'wavelength' and 'velocity' of a sound wave. What is the relation between them?

When a wave travels through a medium, particles of the medium oscillate about their mean position. The number of oscillations per second is known as the frequency of the wave. SI unit of frequency is Hertz(Hz).

The distance between two consecutive crests or troughs is called wavelength of the wave. SI unit of wavelength is meter (m). It is denoted by symbol 'λ'.

When a wave travels through a medium, it creates a disturbance in the particles of the medium. As the disturbance moves along the direction of the wave, we say the wave is moving. The distance covered by that disturbance in one second is known as the velocity of the wave. It is given by the product of the wavelength and frequency of the wave.

Wavelength, Frequency, and velocity of any wave are related according to the following relation,

#### Question 13:

What are the advantages of composite fish culture?

The advantages of composite fish culture are as follows:
1. High amount of fish production can be obtained by this method.
2. This method is economically feasible.
3. The nutrients and food present in the pond are effectively utilised in this method of fish culture.
4. Different varieties of fishes can be produced by this method.

#### Question 14:

Explain the general ways of preventing infection.

The general ways of preventing infections are as follows:
1. Personal hygiene should be maintained to decrease the chances of infections.
2. The surroundings and environment should be kept clean to prevent infections.
3. A healthy lifestyle should be followed to reduce risk of infections.
4. Individuals should be properly vaccinated to decrease prevalence of infectious diseases.

#### Question 15:

Why is the atmosphere essential for life?

Atmosphere refers to the gaseous envelope which is composed of different types of gases. Atmosphere is important for the life because of the following reasons:
1. It forms a protective covering around the Earth and protects living organisms from harmful solar radiations.
2. It also maintains a steady temperature state and prevents abrupt temperature fluctuations.
3. It also supports life by providing the gases which are essential for the survival of organisms.

#### Question 16:

Explain the formation of (i) sodium ion, and (ii) chloride ion, from their respective atoms giving the number of protons and number of electrons in each one of them. What is the reason for positive charge on a sodium ion and negative charge on a chloride ion?

(i) Electronic configuration of sodium (Na) is 2, 8, 1.
To attain noble gas configuration sodium atom will lose one electron and form sodium ion. Sodium gets a positive charge on it as it loses one electron.

Na = 2, 8, 1
Number of protons = 11
Number of electrons = 11

Na+ = 2, 8
Number of protons = 11
Number of electrons = 10

(ii) Electronic configuration of chlorine (Cl) is 2, 8, 7. To attain noble gas configuration chlorine atom will gain one electron and form chloride ion. Chlorine gets a negative charge on it as it gains one electron.
Cl = 2, 8, 7
Number of protons = 17
Number of electrons = 17

Cl- = 2, 8, 8
​Number of protons = 17
Number of electrons = 18

#### Question 17:

(a) Define valency of an element. What valency will be shown by an element having atomic number 14?
(b) What is the relation between the valency of an element and the number of valence electrons in its atoms? Explain with examples.

(a) Valency of an element can be defined as the number of electrons present in the valence shell that is/are available for bonding.
Electronic configuration of the element having atomic number 14 is 2, 8, 4.
As this element has 4 electrons in its valence shell it's not possible to lose 4 electrons, so valency of this element is 4.

(b) Valency of an element is the number of electrons available for bond formation while valence electrons are electrons available in the outer most shell of the atoms.

For eg.,
Electronic configuration of chlorine is 2, 8, 7.
Valence electrons = 7
Valency of chlorine = 1

Electronic configuration of aluminium is 2, 8, 3.
Valence electrons = 3
Valency of aluminium = 3

#### Question 18:

(a) Define density. What is the SI unit of density?
(b) Define relative density. What s the SI unit of relative density?

(a) The density of a body is defined as the mass per unit volume of the body.

The SI unit of the density is kg/m3

(b) The density of a body relative to the density of the water is known as the relative density of the body. It is basically the ratio of the density of a body to the density of water.

Relative density is a unitless quantity, as it is given by the ratio of densities.

#### Question 19:

(a) Define the term 'energy' of a body. What is the SI unit of energy.
(b) What are the various forms of energy?
(c) Two bodies having equal masses are moving with uniform speeds of v and 2v respectively. Find the ratio of their kinetic energies.

(a) Energy of a body is defined as the capacity of the body to do work. Its SI unit is Joule and it is represented as 'J'.

(b) Following are some of the forms of energy:

Thermal energy, chemical energy, electric energy, electromagnetic energy, nuclear energy, magnetic energy, mechanical energy, sound energy, etc.

(c) The kinetic energy of a body of mass 'm', moving with a velocity 'v' is given by $\frac{1}{2}m{v}^{2}$.

As both the bodies have equal masses, let's say 'M', then the ratio of their kinetic energies = $\frac{{\left(K.E.\right)}_{1}}{{\left(K.E.\right)}_{2}}=\frac{\frac{1}{2}M\left(v{\right)}^{2}}{\frac{1}{2}M\left(2v{\right)}^{2}}=\frac{v{}^{2}}{4{v}^{2}}=\frac{1}{4}$

Hence, the ratio of kinetic energies of both bodies is 1:4.

#### Question 20:

What are pisces? Classify and explain two different kinds of fishes by the help of suitable examples.

Pisces is a superclass which comprises all types of fishes. Pisces are further categorised into two classes. These classes are as follows:

1. Class Chondrichthyes: The body of these organisms is covered with placoid scales and they possess a cartilagenous skeleton. These organisms show internal fertilization and tail fins are assymtrical. External ears are absent in these organisms and operculum over the gills is absent. Examples of organisms belonging to class  Chondrichthyes are Scoliodon, Pristis, Sphyrna and Chimaera.

2. Class Osteichthyes: The body of these organisms is covered with cycloid scales and they have a bony skeleton. The tail fins of these organisms are symmetrical and operculum is present over the gills. These organisms show external fertilization. Some of the examples of organisms belonging to class  Osteichthyes are Labeo, Anabas, Hippocampus and Exocoetus.

#### Question 21:

Give an account of some important viral diseases of human beings.

Some of the most important viral diseases of humans have been explained as follows:

1.Influenza: Influenza is also referred to as flu and is caused by the infection of Myxovirus influenza. Influenza virus exist into three forms namely A, B and C type of viruses. This disease primarily spreads through direct contact with an infected person and by droplet infection. Common symptoms of this disease include coughing, general weakness, inflammation of respiratory mucosa and nasal discharge.

2. Hepatitis: Hepatitis is a disease which affects the functioning of the liver. This disease can be caused by different strains of Hepatitis virus including Hepatitis A, B, C, D and G. Common symptoms of hepatitis include loss of appetite, dark yellow urine and light coloured stools.

3. Rabies: Rabies is caused by Lyssa virus and it is actively transmitted by the bite of a rabid dog or other rabid organisms. This disease is characterised by severe headache, painful muscle contraction and high fever.

4. Acquired Immunodeficiency Syndrome (AIDS): AIDS is caused due Human Immunodeficiency Virus (HIV) and it is primarily transmitted by exchange of body fluids through sexual contact and blood transfusions.

#### Question 22:

Tincture of iodine is a mixture of two materials X and Y. The material Y has a property that its solid form can be converted directly into vapours on heating by a process called Z.
(a) What could X be?
(b) What could Y be?
​(c) Name the process Z.

Tincture of iodine is prepared by dissolving proper amount of iodine in an alcohol solution.

(a) So X could be alcohol.

(b) So Y could be iodine.

(c) When the solid phase directly converts to gas phase on heating, it is known as sublimation. So, process Z is sublimation.

#### Question 23:

Calculate the number of aluminium ions present in 0.051 g of aluminium oxide (Al2O3). (Atomic masses: Al = 27 u; O = 16 u)

As 1 mole of aluminium oxide contains 2 moles of aluminium.

So, 0.0005 mole of aluminium oxide contains = 0.0005 ⅹ 2

0.0005 mole of aluminium oxide contains = 0.001 mole of Aluminium

As 1 mole contains 6.022 ⅹ 1023 ions
Therefore, 0.001 moles of aluminium oxide = 6.022 ⅹ 1023 ⅹ 0.001 ions
=  6.022 ⅹ 1020 ions of aluminium

Hence, 0.051 g of aluminium oxide contains 6.022ⅹ1020 ions of aluminium.

#### Question 24:

A girl is wearing a pair of flat shoes. She weighs 550 N. The area of contact of one shoe with the ground is 160 cm2. What pressure will be exerted by the girl on the ground if she stands on two feet?

According to relation,

Force of gravity = Weight of the girl = 550 N

Area of contact of one shoe = 160 cm2

Area of contact for both shoes = 320 cm= 3.2 $×$ 10$-$2 m2

$\therefore$ Pressure =

#### Question 25:

If the work done by a force in moving an object through a distance of 20 cm is 24.2 J, what is the magnitude of the force?

Work done by a force is defined as the product of the force and the displacement.

Work done, $W=F×s$

Work done = 24.2 J

Displacement = 20 cm = 0.2 m

Hence, the magnitude of the force is 121 N.

#### Question 26:

(a) Identify the organism in the following figure.
(b) Label the parts numbers 1 to 4.
(c) Name the phylum in which notochord is present.
(d) Name the subphylum in which notochord is present throughout life.

(a) The given figure represents Amphioxus (Branchiostoma).

(b) In the given figure,
1 - represents nerve cord
2 - represents notochord
3 - represents atriopore and
4 - represents oral hood

(c) Organisms belonging to the phylum Chordata have notochord.

(d) Organisms of the subphylum Cephalochordata retain notochord throughout their lives.

#### Question 27:

Government has recently taken series of steps to minimise cigarette smoking and tobacco chewing by people as these are injurious to health.
(i) List at least three steps taken by government to aware people about harmful effects of cigarette smoking and tobacco chewing.
​(ii) What is passive smoking?