Lakhmir Singh Manjit Kaur Chemistry 2020 2021 Solutions for Class 9 Science Chapter 10 Model Test Paper 5 are provided here with simple step-by-step explanations. These solutions for Model Test Paper 5 are extremely popular among Class 9 students for Science Model Test Paper 5 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 10 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.

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Question 1:

Name the scientist who first studied living cell?


Living cells were first studied by Antonie Van Leeuwenhoek.

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Question 2:

What kills bacteria in our food in the mouth and stomach?


 In mouth, salivary lysozyme kills the bacteria whereas in stomach, hydrochloric (HCl) acid kills bacteria.

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Question 3:

If a balloon filled with air and its mouth untied, is released with its mouth in the downward direction, it moves upwards. Why?


The air filled in the balloon ejects at very high speed, which exerts an upward thrust force on the balloon to conserve the momentum of the whole system. Hence, the balloon moves in an upward direction. 

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Question 4:

When a ball is thrown vertically upwards, its velocity goes on decreasing. What happens to its potential energy as its velocity becomes zero?


When a ball is thrown in an upward direction, its velocity decreases continuously but its potential energy goes on increasing. As the ball reaches to a maximum height, the kinetic energy gradually gets converted into potential energy of the ball. At the highest point where the velocity of the ball becomes zero, the potential energy of the ball becomes maximum. Because all of the kinetic energy gets converted into potential energy.

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Question 5:

Why it is difficult to develop vaccines for some diseases?


Certain infectious agents such as viruses have a relatively simple structure, but they are able to undergo rapid modifications. These modifications allow these infectious agents to easily evade the immune system and most of the vaccines fail to work against these viruses. Thus, certain infections cannot be effectively treated by vaccination.

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Question 6:

If 2 mL of acetone is present in 45 mL of its aqueous solution, calculate the concentration of this solution.


Volume of solute (acetone) = 2 mL
Volume of solution (solute+solvent) = 45 mL

Concentration of solution=Volume of soluteVolume of solution×100Concentration of solution=245×100Concentration of solution=4.44% 


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Question 7:

What mass of nitrogen, N2, will contain the same number of molecules as 1.8 g of water, H2O? (Atomic masses: N = 14 u; H = 1 u; O = 16 u)


Molecular mass of water=2×H+OMolecular mass of water=2×1+16Molecular mass of water=18
Number of moles of water=mass of watermolar mass of water                                    =1.818                                    =0.1 mol

Mass of 1 mole of nitrogen = Molar mass of nitrogen = 14 g
Mass of 0.1 mole of nitrogen = 14 × 0.1
Mass of 0.1 mole of nitrogen = 1.4 g

So, 1.4 g of nitrogen contains an equal number of molecules as present in 1.8 g of water.

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Question 8:

(a) What are radioactive isotopes? Give two examples of radioactive isotopes.
(b) Give any two uses of radioactive isotopes.


(a) Radioactive isotopes are those isotopes of an element which have an unstable nucleus. Because of this, the radioactive isotopes undergo radioactive decay by emitting alpha, beta, and gamma radiation to gain the stability of the nucleus. For eg, O15, Co60, etc.

(b) Uses of radioactive isotopes:
(i) Radioactive isotopes are used to determine the age of rocks and minerals.
(ii) It is used to treat cancer, detect blood clots and diagnose thyroid.

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Question 9:

A ball X of mass 1 kg travelling at 2 m/s has a head-on collision with an identical ball Y at rest. X stops and Y moves off. Calculate the velocity of Y after the collision.


By conservation of momentum,
Total momentum before the collision =  Total momentum after the collision

Mass of the ball X, MX = 1 kg

The velocity of the ball X before the collision, uX = 2 m/s

The velocity of the ball X after the collision, vX = 0 m/s

Mass of the ball Y, MY =1 kg

The velocity of the ball Y before the collision, uY = 0 m/s

The velocity of the ball Y after the collision, vY = v

Using conservation of momentum, MXuX+MYuY=MXvX+MYvY

1 kg×2 m/s + 1 kg×0=1 kg×0 + 1 kg×vv=2 m/s

Hence, the velocity of ball Y, after the collision is 2 m/s.

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Question 10:

Name these forces:
(a) the upward push of water on a submerged object
(b) the force which wears away two surfaces as they move over one another
(c) the force which pulled the apple off Isaac Newton's tree.


(a) When a body is submerged in water, it feels an upward push. That upward push of the water on the body is known as Buoyant force.

(b) When two rough surfaces come in contact, they move over one another, the force involved is known as Frictional force.

(c) The force which pulled the apple off is the gravitational force of attraction of the earth. It always acts downwards, towards the center of the earth.

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Question 11:

When a ball is thrown inside a moving bus, does its kinetic energy depend on the speed of the bus? Explain.


Yes, the kinetic energy of the ball depends upon the speed of the bus. When we are sitting on a bus, we are actually moving along with the bus with a speed equal to the speed of the bus. So, if we are holding a ball, that already means that the ball also has the same speed as ours or the same as the bus. This simply means that the ball and we both are a part of the system, which is moving at the same speed as the speed of the bus. So, if the speed of the bus changes then the speed of the ball changes too.

When we throw a ball inside the bus with some speed, then we are just going to provide some extra speed to the ball along with the speed of the bus. But this can only be observed by a person standing outside the bus, i.e. a stationary observer (with respect to the earth). If the observer would be inside the bus, then he would also become a part of the system which is moving with a speed same as the speed of the bus, then the observer will observe the ball with respect to him. 

Hence, we can say that the kinetic energy of the ball depends on the speed of the bus but only if we are a stationary observer (with respect to earth)

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Question 12:

What factors may be responsible for losses of grains during storage?


Loss of grains during storage can occur because of following factors:

1. Biotic factors: During storage, insects, fungi, mites and rodents may grow. The growth of these organisms can lead to grain spoilage, which eventually leads to loss of grains.

2. Abiotic factors: Certain abiotic factors such as temperature and moisture content can promote the growth of microorganisms. This leads to grain spoilage as well as grain loss.

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Question 13:

Match the contents of the column I and II

Column I Column II
1. Photosynthetic tissue a. Transport
2. Epithelial tissue b. Protection
3. Connective tissue c. Message
4. Blood tissue d. Feeding
5. Nervous tissue e. Strength
6. Collenchyma f. Division
7. Bone g. Flexibility
8. Meristem h. Calcium and phosphorus


The correct match for the given terms is as follows:

Column I    Column II
1. Photosynthetic tissue    d. Feeding  
2. Epithelial tissue                    b. Protection  
3. Connective tissue           g. Flexibility
4. Blood tissue                       a. Transport
5. Nervous tissue                      c. Message
6. Collenchyma                        e. Strength
7. Bone                                      h. Calcium and phosphorous
8. Meristem                               f. Division

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Question 14:

List a few flight adaptations in birds.


Some of the flight adaptations in birds are as follows:

1. Some of the bones of birds are hollow, which makes them lightweight and allows them to fly.

2. The forelimbs of birds have been modified into wings, which assist in flying.

3. The body of birds is streamlined, which decreases air resistance.

4. The flight muscles in birds are very strong.

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Question 15:

How do organisms contribute in the formation of soil?


Living organism contribute to the formation of soil by performing biological weathering. In biological weathering, the living organisms secrete chemical secretions that help in the breakdown of large rocks into smaller fragments. Typical examples of organisms that help in soil formation are Lichens and Bryophytes.

Lichens induce biological weathering by extracting minerals from the rocks, which results in the formation of small cervices that serve as the site for soil formation.

Bryophytes can readily grow in the cervices formed by lichens and further deepen the cervices. These deeper cervices form cracks. In due course of time, because of growth of bigger plants, rocks eventually pulverise and form soil.

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Question 16:

(a) Define the term 'latent heat of fusion' of a solid. How much is the latent heat of fusion of ice?
​(b) Draw a labelled diagram of the experimental set-up to study the latent heat of fusion of ice.


(a) Latent heat of fusion is the heat required to change 1 kg of solid substance into the liquid state at the melting point of the substance. For eg. amount of heat required to melt ice at 0 °C into the water at 0 °C, will be known as the latent heat of fusion of ice.
For ice, the latent heat of fusion is 334 kJ kg-1. This means that 334 kJ of heat is required to convert 1 kg of ice at 0 °C into 1 kg of water at 0 °C.

(b) Experimental setup to study the latent heat of fusion of ice:


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Question 17:

(a) What are valence electrons? Where are valence electrons situated in an atom?
​(b) What is the number of valence electrons in the atoms of an element having atomic number 13? Name the valence shell of this atom.


(a) Valence electrons are electrons present in the outermost orbital of the atom. They basically represent the number of electrons which can participate in bond formation.
Valence electrons are present in the outermost orbit.

(b) Electronic configuration of the element with atomic number 13 is 2, 8, 3.
So, the valence electrons present in this element are 3.

2      8      3K     L     M

The valence shell of the atom will be M.

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Question 18:

(a) State and explain the law of conservation of energy with an example.
​(b) Explain how, the total energy a swinging pendulum at any instant of time remains conserved. Illustrate your answer with the help of a labelled diagram.


(a) In physics, the law of conservation of energy states that the total energy of an isolated system remains constant or conserved over time. It also says that the energy can neither be created nor be destroyed, but it can be changed from one form to another.

The law of conservation of energy can be seen in the following example of energy transference:

In a hydroelectric plant, the potential energy of the water stored at some height is converted into kinetic energy by setting it into motion. Then the water falls upon the turbine and the turbine rotates. So, the kinetic energy of the water gets converted into mechanical energy. That mechanical energy is used to generate electricity out of a generator attached to the turbine. Hence, the total energy remains conserved, but it changed from one form to another throughout the process. 

(b) When a pendulum is stationary, it remains at its mean position or center position as shown in the figure. If the bob of the pendulum is lifted towards one side, then it gains some potential energy. Now, if the bob is left from one of the extreme positions then it will start swinging about the mean position, up to left extreme position then back again at the right extreme position passing through mean position every time.

At both the extremes, the energy possessed by the bob is purely potential. But, when the bob goes down, the potential energy gradually converts into kinetic energy and at the mean position where potential energy becomes zero, the bob has the maximum kinetic energy. That simply means the whole of the potential energy gets converted into kinetic energy at the mean position. In between the motion, the bob has both kinetic and potential energy but the total energy always remains constant or conserved throughout the motion. 

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Question 19:

(a) Explain the terms 'crests' and 'troughs of a wave? What type of waves consist of crests and troughs?
​(b) The flash of a gun is seen by man 3 seconds before the sound is heard. Calculate the distance of the gun from the man (Speed of sound in air is 332 m/s).


(a) When a wave travels through a medium, the particles of the medium oscillate about their mean position, up and down. The maximum displacement of the particles above the mean position is referred to as a 'Crest' and the maximum displacement below the mean position is referred to as a 'Trough'. All the transverse waves consist of crests and troughs. 

(b) Let the distance of the man from the gun = d

Speed of the light = 3×108 m/s

Speed of the sound = 332 m/s

Let the time taken by the sound to reach the man =  = d332 .......(1) 

Then the time taken by the light to reach the man = t-3 = d3×108  ........(2)

Putting the value of 't' from equation (1) into equation (2), we get,

d332-3=d3×108d332-d3×108=33×108-3323×108×332 d = 3(0.003) d =3d =1000 m

Hence, the distance of the man from the gun is 1000 m.

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Question 20:

Write short notes on
​(a) Tuberculosis; (b) Polio.


(a) Tuberculosis: Tuberculosis is caused by the infection of bacterium called Mycobacterium tuberculosis. This disease can be transmitted from one organism to another through indirect or direct contact. The common symptoms of tuberculosis include weakness, loss of apetite, weight loss and fever. This disease is treated by the administration of antibiotics such as Streptomycin and Rifampicin.

(b) Polio: Polio is a viral disease which primarily affects the nervous system. This disease is caused by polio virus. This virus destroys the motor neurons present in the spinal cord which regulate muscles. The destruction of these neurons result in a paralytic condition. Early symptoms of polio include headache and soar throat. Polio can be prevented by administration of Oral Polio Vaccine (OPV).

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Question 21:

Explain the following:
​(i) Eutrophication; (ii) Biomagnification.


(i) Eutrophication: Eutrophication is characterised by the excessive algal growth in water bodies such as ponds. This excessive growth is primarily caused due to the over enrichment of the water body with nutrients which occur due to agricultural runoff and water pollution. The algal growth depletes the oxygen content of the lake and severely affects the lives of aquatic organisms.

(ii) Biomagnification: Biomagnification is a process in which the concentration of a non-biodegradable substance such as insecticide progressively increases from one trophic level to another. These non-biodegradable substances primarily accumulate in the fatty tissues of organisms and when an organism of higher trophic level consumes another organism, these substances are propagated to next trophic level.

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Question 22:

If the back of your hand is moistened with alcohol, you will find that it rapidly becomes dry. Why is it that while it is drying, your hand feels cool?


The alcohol absorbs latent heat of vaporization from the surface of our hands and evaporates. Drawing heat and therefore, cooling our hand in the process.

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Question 23:

A student wants to have 3.011 × 1023 atoms each of magnesium and carbon elements. For this purpose, how much magnesium and carbon will he weigh in grams?


12 g of carbon and 24.3 g of magnesium, each contains 6.022×1023 number of atoms.
Let X g of carbon have 3.011×1023 number of atoms.
X=molar mass of carbon×number of atoms of carbonAvogadro numberX=12×3.011×10236.022×1023X=6 g of carbon
So, 6 g of carbon contains 3.011×1023 number of atoms.

Let X g of magnesium have 3.011×1023 number of atoms.
X=molar mass of magnesium×number of atoms of magnesiumAvogadro numberX=24×3.011×10236.022×1023X=12 g of magnesium
So, 12 g of magnesium contains ​3.011×1023 number of atoms.

Hence, he will weigh 12 g of magnesium and 6 g of carbon.

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Question 24:

Show by means of a graphical method that: v  = u + at where the symbols have their usual meanings.


Let's suppose 'u' is the initial velocity of a body and 'v'  is the final velocity of a body after time interval 't'. As you can see in the figure given below.

Then, acceleration 'a' of the body can be written as,

= Slope of the velocity-time graph 

 a=v-ut-0at = v-uv=u + at (1st equation of motion)

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Question 25:

The echo of a sound is heard after 5 seconds. If the speed of sound in air be 342 m/s, calculate the distance of the reflecting surface.


An echo is heard when a sound hits any hard surface and the reflected sound reaches back to our ears. 

Let the distance of the reflecting surface = d

Speed of the sound in air = 342 m/s

Time taken by an echo to be heard = 5 seconds

Total distance travelled by the sound waves = 2d

2d =342 m/s × 5 sd = 342 m/s × 5 s2=855 m

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Question 26:

What will happen if all RBCs are removed from the blood?


Red Blood Cells (RBCs) contain haemoglobin protein, which is responsible for transportation of oxygen throughout the body. In case all RBCs are removed from the blood, the oxygen transport capacity of blood will be severely affected. The tissues and organs will not get the required amount of oxygen and the organism will eventually die.

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Question 27:

"We can treat an infectious disease by killing microbe". Justify the statement with suitable examples.


Infectious diseases can be effectively treated by eliminating the microbes. This is because microbes are the causative agents for infectious diseases. Thus, the given statement is correct. A typical example in this context can be observed in the case of tuberculosis. The administration of Rifampicin kills Mycobacterium tuberculosis which is used as a treatment for tuberculosis.

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