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Page No 365:

Question 1:

Which organ secretes a hormone when the blood sugar rises? Name a digestive enzyme released by this organ.


 Pancreas secrete insulin when the blood sugar rises. It also produces the enzyme trypsin in an inactive form called trypsinogen.

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Question 2:

Metals generally occur in solid state. Name and write symbol of a metal that exists in liquid state at room temperature.


Metals generally occur in the solid state but mercury is the only metal in the periodic table which exists in the liquid state at room temperature. Symbol of mercury is Hg.

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Question 3:

Study carefully the food chain given below:
Food chain: wheat → rat → snake → hawk
To which of the two consumers, snake or hawk, will more energy (per cent) be available and why?


Wheat →rat →snake →hawk
In the above food chain, more energy will be available to snake than hawk. Energy transfer from one trophic level to another follows 10% law of energy transfer.
According to this law, only 10% of the energy stored at a particular trophic level is transferred to the next higher trophic level.

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Question 4:

The following table gives the values of refractive indices of a few media.

S.No. 1 2 3 4 5
Medium Water Crown Glass Rock salt Ruby Diamond
Refractive index 1.33 1.52 1.54 1.71 2.42
Use this table to give an example of (i) a medium pair so that light speeds up when it goes from one of these media to another (ii) a medium pair so that lights slows down when it goes from one of these media to another.​


Speed of light increases when it travels from denser to rarer medium and it decreases when it travels from rarer to denser medium. Because in a denser medium more particles get in the way. Any medium with a greater value of the refractive index is an optically denser medium with respect to a medium with a smaller value of the refractive index.

(i) If we take a pair of Diamond and crown glass, then the crown glass is rarer medium with respect to the diamond as it has a less refractive index as compared to diamond. Now if light travels from diamond into the crown glass, it would speed up as it has to travel through a less dense medium. 

(ii) If we take a pair of water and crown glass, then the crown glass is denser than the water as it has a more refractive index as compared to water, so the speed of the light would decrease if it travels into crown glass from the water.

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Question 5:

Tooth enamel is one of the hardest substances in our body. How does it undergo damage due to eating chocolates and sweets? What should we do to prevent it?


Tooth enamel is made of calcium phosphate. It does not dissolve in water but it starts corroding when the pH in the mouth decreases to 5.5 or less. When we eat chocolates, small pieces of these stick to our teeth. The bacteria present in our teeth start decaying the food particles as a result of which small amount of acid is produced. This acid, decreases the pH of the mouth and results in the decaying of tooth enamel.

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Question 6:

Explain the following:
​(a) Why is tungsten used almost exclusively for filament of electric lamps?
(b) Why are copper and aluminium wires usually used for electricity transmission?
​(c)Why is nichrome alloy used for making elements of electric irons?


(a) Tungsten is used for the filament of electric lamps because it has a very high melting point, so it does not melt when the electricity is passed through it. That's why the temperature of the wire can be increased to a high value without melting the wire. Higher the temperature of the filament whiter the light.

(b) Copper and aluminium wires are the good conductors of electricity, as they have a very low resistivity. Low resistivity decreases the resistance of transmission wires and hence increases the amount of current flow in the circuit. 

(c) The nichrome wire is used for making the elements of electric irons because it has a very high resistivity along with a very high melting point, which makes it perfect as a heating element of the electric appliances. 

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Question 7:

A household uses the following electric appliances:
(a) Refrigerator of rating 400 W for ten hours each day.
​(b) Two electric fans of rating 80 W each for twelve hours each day.
(c) Six electric tubes of rating 18 W each for 6 hours each day.
Calculate the electricity bill of the household for the month of June if the cost per unit of electric energy is â‚¹ 3.00.


1 unit of energy equals 1 kilowatt-hour. 

(a) Units spent in a day by refrigerator = 400 W × 10 h = 0.4 kW × 10 h = 4 kWh = 4 units

(b) Units spent in a day by two electric fans = (80 × 2) W × 12 h = 0.16 kW × 12 h = 1.92 kWh = 1.92 units

(c) Units spent in a day by six electric tubes = (18 × 6) W × 6 h = 0.108 kWh × 6 h = 0.648 kWh = 0.648 units

Total units spent in a day = 4 + 1.92 + 0.648 = 6.57 units

Total units spent in the month of June = 30×6.57 units = 197 units

Total cost in a month = 197 × 3 = ₹ 591  

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Question 8:

Why does a current carrying conductor kept in a magnetic field experience force? On what factors does the direction of this force depend? Name and state the rule used for the determination of the direction of this force. 


A current carrying wire also creates its own magnetic field, so when it is placed in an external magnetic field then due to the interaction between the external magnetic field and its own magnetic field the wire feels a force.

The direction of the force depends on the direction of the current and the direction of the magnetic field.

The direction of the force on the current carrying conductor is obtained with the help of Fleming's left-hand rule. Fleming's Left Hand Rule states that whenever a current carrying conductor is placed inside a magnetic field, a force acts on the conductor, in a direction perpendicular to both the directions of the current and the magnetic field.

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Question 9:

Two metallic wires A and B are connected in parallel. Wire A has length l and radius r, wire B has a length 2l and radius 2r. Compute the ratio of the total resistance of parallel combination and the resistance of wire A.


The resistance of a wire is directly proportional to its length and inversely proportional to the area of cross-section of the wire.

R lAlr2

Wire A has length l and radius r, wire B has a length 2l and radius 2r. So, we can say, 

RARB=lr2×(2r)22l=21  .....(1)

Net resistance in parallel combination = RARBRA+RB=RARARB+1=RA3 RARB=2

The ratio of the total resistance of parallel combination and the resistance of wire A = RA3RA=13

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Question 10:

Answer the following:
(a) Why is plaster of Paris written as CaSO4.12H2O? How is it possible to have half a water molecule attached to CaSO4?
(b) Why is sodium hydrogencarbonate an essential ingredient in antacids?
(c) When electricity is passed through an aqueous solution of sodium chloride, three products are obtained. Why is the process called chlor-alkali?


(a) Calcium sulphate hemihydrate or plaster of paris is formed when gypsum is heated at a temperature of 373K.
Plaster of paris is written in this form to show that two molecules of calcium sulphate combine with one molecule of water. Thus, each calcium sulphate molecule gets only half the share of the water molecule and hence, hemihydrates.

(b) The excess of acid in the stomach causes acidity. As sodium bicarbonate is alkaline in nature, it neutralizes the excess acid and relieves discomfort. Hence, it is an essential ingredient in antacids.

(c) When electricity is passed through an aqueous solution of sodium chloride it decomposes to form sodium hydroxide, chlorine gas, and hydrogen gas.

This process is called the chlor-alkali process because of the products formed chlor- for chlorine and alkali for sodium hydroxide.

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Question 11:

Baking soda is used in small amount in making bread and cake. It helps to make these soft and spongy. An aqueous solution of baking soda turns red litmus blue. It is also used in soda acid fire extinguisher.
Use this information to answer the following questions:
(a) How does baking soda help to make cakes and bread soft and spongy?
(b) How does it help in extinguishing fire?
​(c) Is the pH value of baking soda solution lesser than or greater than 7?


(a) Baking soda reacts with the acidic ingredients of bread and cake to form carbon dioxide gas which makes the foodstuff to rise and thus makes it soft and spongy.

(b) Soda acid fire extinguishers contain a mixture of sulphuric acid and baking soda. They react to release carbon dioxide which forms a layer over the burning substance and cuts the supply of oxygen of the fire.

(c) The pH of baking soda solution is greater than 7 since, it is a salt of a strong base, NaOH and a weak acid, H2CO3.

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Question 12:

Atomic number is considered to be a more appropriate parameter than atomic mass for the classification of elements in a periodic table. Why?
How does atomic size of elements vary on moving from:
(i) left to right in a period?
(ii) top to bottom in a group?
​Give reasons for your answers.


The properties of elements depend upon their valence electrons which in turn depends on the total number of electrons, i.e., atomic number. Therefore, atomic number is considered to be a more appropriate parameter than atomic mass for the classification of elements.

(i) On moving from left to right in a period, the atomic size decreases due to an increase in nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom.

(ii) On moving from top to bottom in a group, atomic size increases because new shells are being added as we go down the group. This increases the distance between the valence shell and the nucleus.

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Question 13:

Study the given data and answer the questions following the data.

Parental plants cross fertilised and seeds collected F1 (first generation offspring) F2 (offspring of self pollination of F1)
Male parent always bore red flowers. 330 seeds sown and observed Out of 44 seeds, 33 seeds gave plants with red flowers and 11 seeds gave plants with white flowers
Female parent always had white flowers. All 330 gave red flowers  
(a) What is the term for this type of cross?
(b) What does the data of the column marked F1 indicate?
(c) Express the genotype of the (i) parents (ii) F1 progeny, and (iii) F2 progeny.


(a) It is a monohybrid cross.

(b) The data in column F1 indicates that red coloured flowers are dominant over white coloured flowers.

(c) The genotypes are as follows -
(i) Parents - RR, rr
(ii) F1 progeny - Rr
(iii) F2 progeny - RR, Rr, rr

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Question 14:

Why are environmentalists insisting upon 'sustainable natural resource management? Give any three reasons.


Environmentalists insisting upon "Sustainable natural resource management " because of following reasons :

1. For equal distribution of resources for equal benefits as the majority of natural resources is limited and the human population is increasing at a tremendous rate. 

2. Need to reduce the damage caused to the environment because of the over-exploitation and utilization of resources.

3. Need to conserve resources for future generations.

Thus, a proper and planned utilization of natural resources is essential for sustainable development.

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Question 15:

(a) What is 'Chipko andolan'? How did it originate?
​(b) How did the 'Chipko andolan' ultimately benefit the local population? Give any two benefits.


(a) The Chipko Andolan originated in a remote village in Garhwal, called Reni, during early 1970s. This movement started from an incident of dispute between the local villagers and a logging contractor who had been allowed to cut trees in a forest close to the village. When the contractor's workers went to the forest to cut the trees, the women of the village reached the forest quickly and hugged the tree trunks, thus, preventing the workers from cutting the trees. Ultimately, the contractor had to withdraw. The movement soon became very popular and quickly spread to various communities across the country.

(b) The benefits to the local population from the Chipko andolan are -

  • It helped in the preservation of local traditions, cultures as well as in the environment protection as the people could get basic necessities from the forest such as shelter and food for the cattles.
  • This movement was also helpful in maintaining ecological balance.

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Question 16:

(a) What were the two major shortcomings of Mendeleev's periodic table? How have these been removed in the modern periodic table?
(b) Two elements X and Y have atomic numbers 12 and 16 respectively. Write the electronic configuration for these elements. To which period of the modern periodic table do these two elements belong? What type of bond will be formed between them and why?
(c) To which groups of the modern periodic table do the elements X and Y belong? Give reason for your answer.
(d) What could the elements X and Y be? Write their names and symbols.


(a) Two major shortcomings of Mendeleev's periodic table:
(i) Isotopes position was not confirmed
(ii) Position of hydrogen was doubtful

These anomalies were removed in modern periodic table:
(i) Isotopes were placed with their atoms, as all of them have same atomic numbers.
(ii) Hydrogen was assigned a position at the top of the period which is different but its nature matches with the group elements.

(b) Electronic configuration of X = 2, 8, 2 and Y = 2, 8, 6.
Both of them belong to the third period of the modern periodic table because three shells available in both of them.
To achieve noble gas configuration X will lose electrons while Y will gain electrons. So, they will form an ionic bond.

(c) X has two valence electrons so it comes under alkaline earth metal family (1) and Y has 6 valence electrons so it comes under oxygen family (16).

(d) Electronic configuration of X resembles magnesium (Mg) while the electronic configuration of Y resembles sulphur (S). So the ionic compound formed will be of XY type i.e. MgS.

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Question 17:

(a) What is meant by 'allotropes'? Name the various allotropes of carbon.
(b) Why does carbon form largest number of compounds?
(c) Why are some of these called saturated and other unsaturated compounds?
(d) Which of these two is more reactive? Give reason for your answer.
(e) Write the names of the following compounds:


(a) Allotropes are the different physical forms of the same element. Carbon has three different allotropic forms diamond (C4), graphite (C3) and Buckminsterfullerene (C60).

(b) Carbon forms the largest number of compounds because of its two properties -

1. Catenation − This is the property of carbon atoms to form bonds with other carbon atoms.
2. Tetravalency − A carbon atom forms four covalent bonds. Moreover, it can form stable single, double and triple bonds with a lot of elements.

(c) Molecules having a single bond are known as a saturated hydrocarbons, for example - alkanes.
Molecules having a double or triple bond are known as an unsaturated hydrocarbon, for example - alkenes and alkynes.

(d) Unsaturated hydrocarbons are more reactive than saturated hydrocarbons. Unsaturated hydrocarbons have double or triple bonds which are weaker compared to the single bonds of saturated hydrocarbons. These double and triple bonds act as reactive sites where addition reactions can occur easily.

(i)  1-Bromoethane

(ii) Hex-1-yne

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Question 18:

A student finds the writing on the blackboard as blurred and unclear when sitting on the last desk in the classroom. He, however, sees it clearly when sitting on the front desk at an approximate distance of 2 m from the blackboard. Draw ray diagrams to illustrate the formation of the image of the blackboard writing by his eye-lens when he is seated at the (i) last desk (ii) front desk. Name the kind of lens that would help him to see clearly even when he is seated at the last desk. Draw a ray diagram to illustrate how this lens helps him to see clearly.


The student is suffering from the Near-sightedness or Myopia. That's why he is able to see blackboard writing when he is nearby the blackboard, but he is unable to see the blackboard writing clearly when he is sitting far at the last desk. 

(i) When he is sitting at the last desk, the image of the blackboard writing is forming in front of the retina due to myopia effect. That's why he is seeing a blurred and unclear image. The following ray diagram explains the defect of the student.

(ii) When the student is sitting on the front desk, he is able to see the writing on the blackboard because his eye is forming the image of the nearby object on the retina. That's why he is able to see the blackboard clearly. The following diagram shows the image formation by his eye when he is sitting on the front desk:

The student must use a concave lens to correct the defect of his eye. The concave lens will diverge the rays coming from the blackboard and will form an image on the retina when he will be seeing the blackboard from a far distance. i.e. Last desk of this class. The following figure shows, how a concave lens can help him to see clearly.


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Question 19:

Explain the meaning of the words 'electromagnetic' and 'induction' in the term electromagnetic induction. On what factors does the value of induced current produced in a circuit depend? Name and state the rule used for determination of the direction of induced current. State one practical application of this phenomenon in everyday life.


The word "electromagnetic" means that an electric potential dipole is being produced in a coil due to change in the magnetic field. The word "induction" means that the current has been induced.

The value of induced current produced in a circuit depends on the following factors :

(1) Number of turns in a given coil.
(2) Area of each turn in a coil.
(3) Rate of change of magnetic field

The direction of the induced current is determined by the flaming right-hand rule. It states that when the thumb, the first and the second fingers on the right hand are held so that they are at right angles to each other, and the first finger points in the direction of the magnetic field and the thumb in the direction of the motion of the conductor then the second finger will point in the direction of the induced current in the conductor.

The electrical generator is the practical application of this phenomenon in everyday life.  

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Question 20:

(a) Name the various organs of the circulatory system in humans.
(b) Draw the diagram of heart and label its four chambers.
​(c) Construct a table to show the functions of these four chambers.


(a) The human circulatory system consists of a muscular four-chambered heart, a network of branching blood vessels and blood. The blood vessels are of three types namely; veins, arteries and capillaries.



Right atrium
Right ventricle Left atrium Left ventricle
Receives deoxygenated blood
from veins and pumps it to the right ventricle.
Receives deoxygenated blood and passes it to lungs to remove the carbon dioxide and increase the concentration of oxygen. Left atrium receives the oxygenated blood from the lungs and passes it to the the left ventricle. Left ventricle receives the oxygenated blood and passes it to the rest of the body.

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Question 21:

(a) Trees absorb water from the soil. How does this water reach the tree tops? Explain in detail.
​(b) Describe the cuttings method for the artificial propagation of plants. Illustrate your answer with the help of labelled diagrams.


(a) The water absorbed by the roots of the trees is transported to different parts of the plant through vascular bundles. The vascular bundles that help in the transportation of water are xylem. These help in the movement of water from roots to tree tops.

(b) In cutting method, a part of stem comprising buds on it is cut from the plant using a sharp knife. The stem is then buried in a suitable medium. After some days, the stem develops roots and starts growing into a new plant. The process of cutting can be illustrated as follows:


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Question 22:

Two students perform the experiments on series and parallel combinations of two given resistors R1 and R2 and plot the given V-I graphs.
Which of the graphs is (are) correctly labeled in terms of the word 'series' and 'parallel'? Justify your answer.



According to Ohm's law, V =IR 

It can be written as, VI=R or IV=1R (Where 'R' is a constant and is known as the resistance of the circuit)

Now, if we draw a graph between voltage and current then the slope of the graph would be the resistance of the circuit if we put current on the x-axis and it would be reciprocal of the resistance if we put voltage on the x-axis. 

In the first graph, the slope is given by the resistance 'R' of the circuit. As we know, the net resistance of the series combination is more than the net resistance in parallel combination. So, the slope for series combination would be more than the slope for parallel combination. Thus, the first graph is correct.

In the second graph, the slope is given by the reciprocal of the resistance 'R'. As we know, the net resistance of the series combination is more than the net resistance in parallel combination. So, the slope for the series combination would be less than the slope for the parallel combination. Thus, the second graph is correct too.

Hence, both graphs are correctly labelled. 

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Question 23:

Two students made box-type solar cookers separately. They both painted the insulated box with black colour from inside, the cooking pots were painted black from outside, and a plane mirror reflector was also attached. One of the students covered the solar cooker box with a transparent glass sheet but the other student covered the solar cooker box with a transparent plastic sheet. Which of the two solar cookers will be more efficient and why?


The solar cooker with a transparent glass sheet will be more efficient because light rays after passing through glass sheet will get absorbed by the black walls of the box. The light will trap inside the box and the temperature will rise. The glass sheet will also prevent the radiation of the heat outside, so the temperature inside the box would be sufficient to cook the food. Whereas, in a solar cooker with a transparent plastic sheet, the heat will radiate outside and the temperature inside the box will never maintain to cook the food properly.

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Question 24:

A student warmed a neutral organic compound with some ethanoic acid and a little of concentrated sulphuric acid in a test-tube. He observed that vapours having sweet smell (fruity smell) are evolved.
(a) What type of functional group is present in this organic compound?
(b) Give the name and formula of one such organic compound.


(a) The functional group present in the organic compound is hydroxyl group. Fruity smell of the vapours produce indicates the presence of ester group. As ester is a result of condensation reaction between alcohol and carboxylic acids.

(b) For example - ethanol reacts with ethanoic acid/carboxylic acid to produce ethyl ethanoate/ester which has a functional group (COO).

C2H5OH+CH3COOHH2SO4CH3COOC2H5Ethyl ethanoate+H2O

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Question 25:

Bromine water has a red-brown colour due to the presence of bromine in it. A student adds bromine water to a little of cooking oil and butter taken in separate test-tubes.
(a) What will the student observe when he adds bromine water to cooking oil? Give reason for your answer.
​(b) What will the student observe when he adds bromine water to butter? Give reason for your answer.


(a) When a student adds bromine water in cooking oil, bromine water will lose its colour. Cooking oil is unsaturated but it will become saturated by addition reaction with bromine water.

(b) When a student adds bromine water to butter, no change will be observed as butter is saturated and no reaction will occur. 

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Question 26:

A student has been given a chart having the following diagram on it:

Copy this diagram in your answer sheet and write the following labels on it at the appropriate places:
  Male child, Mother's ova, Female child, Father's sperms


The labelled diagram for the given case is as follows:

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Question 27:

A student was told that a particular hormone requires iodine for its synthesis.
(a) Name the endocrine gland which secretes this hormone.
​(b) State the location of this endocrine gland in the human body.


(a) Thyroxine hormone requires iodine for its synthesis. This hormone is produced by the thyroid gland.
(b) The thyroid gland is composed of two lobes located on either side of trachea.

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