Lakhmir Singh Manjit Kaur Physics 2020 2021 Solutions for Class 10 Science Chapter 10 Model Test Paper 3 are provided here with simple step-by-step explanations. These solutions for Model Test Paper 3 are extremely popular among Class 10 students for Science Model Test Paper 3 Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Lakhmir Singh Manjit Kaur Physics 2020 2021 Book of Class 10 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 Physics 2020 2021 Solutions. All Lakhmir Singh Manjit Kaur Physics 2020 2021 Solutions for class Class 10 Science are prepared by experts and are 100% accurate.

#### Question 1:

From the list given below, pick out the items which can be recycled:
Used clothes, polythene carry bags, glass bottles, newspaper

Used clothes and newspaper can be recycled.

#### Question 2:

Alloys are used in electrical heating devices rather than pure metals. Give one reason.

Alloys are used in electrical heating devices rather than pure metals because the resistivity of an alloy is more than the resistivity of pure metal. Also, the melting point of an alloy is high, so it does not melt or oxidize easily even at a higher temperature.

#### Question 3:

A student has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and a green coating on copper coins. Which chemical phenomenon is responsible for these coatings? Write the chemical name of black and green coatings.

The phenomena responsible for the formation of a coating on copper and silver objects is known as corrosion. Silver turns black due to the formation of silver sulphide$\left({\mathrm{Ag}}_{2}\mathrm{S}\right)$ while copper turns green due to the formation of a mixture of copper carbonate and copper hydroxide$\left[\left({\mathrm{CuCO}}_{3}\right).\left(\mathrm{Cu}\left(\mathrm{OH}{\right)}_{2}\right)\right]$.
$2\mathrm{Cu}+{\mathrm{CO}}_{2}+{\mathrm{H}}_{2}\mathrm{O}\to \left[\left({\mathrm{CuCO}}_{3}\right).\left(\mathrm{Cu}\left(\mathrm{OH}{\right)}_{2}\right)\right]$
$2\mathrm{Ag}+{\mathrm{H}}_{2}\mathrm{S}\to {\mathrm{Ag}}_{2}\mathrm{S}+{\mathrm{H}}_{2}$

#### Question 4:

The electrical resistivity of a few materials is given below in ohm-metre. Which of these materials can be used for making element of a heating device?

 A 6.84 × 10−8 B 1.60 × 10−8 C 1.00 × 10−4 D 2.50 × 1012 E 4.40 × 10−5 F 2.30 × 1017

The metals and alloys have very low resistivity in the range of 10-8 Ωm to 10-6  Ωm. So, they are a good conductor of electricity. While insulators have a resistivity of the order of 1012  Ωm to 1017 Ωm. Alloys have generally higher resistivity than its constituent metals and consider good for the heating elements. So, elements C and E are best for making heating elements. While D and F are considered as an insulator and A and B are a good conductor of electricity.

#### Question 5:

The human hand, cat paw and the horse foot, when studied in detail show the same structure of bones and point towards a common origin.
(a) What do you conclude from this?
​(b) What is the term given to such structures?

(a) The structures mentioned above have the same origin but they perform same or different functions in different organisms. This indicates that they have evolved from a common ancestor.
(b) The term given to these structures is homologous structures.

#### Question 6:

Distinguish between the arrangement of elements in Mendeleev's periodic table and Modern periodic table. Which of the two arrangements of elements is better and why?

 Mendleev's Periodic Table Modern Periodic Table 1. Elements are arranged in the increasing order of atomic masses. 1. Elements are arranged in the increasing order of atomic numbers. 2. Position of hydrogen could not be explained. 2. Hydrogen is placed above alkali metals. 3. Elements are placed in 7 groups and 6 periods. 3. Elements are placed in 18 groups and 7 periods. 4. Metals and nonmetals are not separated. 4. Metals and non-metals are separated. 5. Elements with similar property are placed. 5. Elements with same valence shell are present in the same period while elements having the same number of valence electrons are present in the same group.

The modern periodic table arrangement is better because elements are arranged in increasing order of atomic numbers.

#### Question 7:

A compound which is prepared from gypsum has the property of hardening when mixed with a proper quantity of water. Identify the compound and write its chemical formula. Write the chemical equation for its preparation. Mention any one use of the compound.

The compound prepared from gypsum which has hardening property when mixed with water is "Plaster of Paris". The chemical formula of Plaster of Paris is ${\mathrm{CaSO}}_{4}.1}{2}{\mathrm{H}}_{2}\mathrm{O}$.
The balanced chemical equation for the preparation of Plaster of Paris is:
$2{\mathrm{CaSO}}_{4}.2{\mathrm{H}}_{2}\mathrm{O}\stackrel{\mathrm{heat}}{\to }2{\mathrm{CaSO}}_{4}.\frac{1}{2}{\mathrm{H}}_{2}\mathrm{O}+3{\mathrm{H}}_{2}\mathrm{O}$

In hospitals, it is used as a plaster for supporting the broken or fractured bones.

#### Question 8:

Give one example each of a chemical reaction characterised by:
(a) evolution of a gas
(b) formation of a precipitate
(c) change in temperature
​Write equations of the reactions which take place in each case.

(a) When zinc granules react with dilute sulphuric acid in a flask, hydrogen gas is evolved and zinc sulphate solution is formed.
$\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{H}}_{2}{\mathrm{SO}}_{4}\left(\mathrm{aq}\right)\to {\mathrm{ZnSO}}_{4}\left(\mathrm{aq}\right)+{\mathrm{H}}_{2}\left(\mathrm{g}\right)$

(b) When potassium iodide is added to lead nitrate solution (colourless and clear), a yellow precipitate of lead iodide solution is formed.
$\mathrm{Pb}\left({\mathrm{NO}}_{3}{\right)}_{2}\left(\mathrm{aq}\right)+2\mathrm{KI}\left(\mathrm{aq}\right)\to {\mathrm{PbI}}_{2}\left(\mathrm{s}\right)+2{\mathrm{KNO}}_{3}\left(\mathrm{aq}\right)$

(c) When quick lime reacts with water, slaked lime is formed along with release of a large amount of heat, causing a change in temperature in the reaction mixture.
$\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{H}}_{2}\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Ca}\left(\mathrm{OH}{\right)}_{2}\left(\mathrm{aq}\right)+\mathrm{Heat}$

#### Question 9:

"pH has great importance in our daily life". Explain by giving three examples.

pH has great importance in our daily life:

(a) pH and plants:
Plants require a specific pH for growth. It cannot grow in too acidic soils. If soil is too acidic then its pH can be increased by adding lime:
$CaO+{H}_{2}S{O}_{4}\to CaS{O}_{4}+{H}_{2}O$
And on the other hand, if the soil is too alkaline then its pH decreases by adding gypsum.

(b) pH and blood or digestive system:
The pH of blood is tightly regulated in the range of 7.2-7.4 and medium in our stomach is highly acidic(pH = 1.2). Sometimes stomach produces too much hydrochloric acid, it causes irritation or pain.

(c) pH and skin:
The acidic pH of the skin prevents colonisation by bacteria. Thus, it acts as a defense against infection.

#### Question 10:

The ciliary muscles of a normal eye are in their:
(i) most relaxed state    (ii) most contracted state
(a) In which of the two cases is the focal length of the eye-lens more?
(b) In which of the two cases is the power of the eye-lens more?

(a) The focal length of the eye lens is more when the ciliary muscles of a normal eye are in their most relaxed state. In this state the lens becomes thin.

(b) As the power of a lens is inversely proportional to its focal length. Hence, the power of the eye lens would be more when the focal length would be minimum, which happens when ciliary muscles are in the most contracted state. In this case, the lens becomes thick.

#### Question 11:

Draw the circuit diagram of an electric circuit containing a battery of 6 V, a key, an ammeter, a resistor of 4 Ω in series with a combination of two resistors of 8 Ω each in parallel, and a voltmeter across the parallel combination.
(a) Calculate the resistance of the circuit.
(b) Find the current flowing in the circuit.
(c) What will be the voltage across the parallel combination of resistors?

(a) In the circuit, there is a 4-ohm resistor in series with the parallel combination of two 8-ohm resistors.

Total resistance of parallel combination =

So, net resistance of the circuit =

(b) Current in the circuit =

(c) The voltage across the 4-ohm resistor =

So, the voltage across parallel combination =

#### Question 12:

What is geothermal energy? Explain how geothermal energy is used to generate electricity. State two advantages of geothermal energy.

Geothermal energy is the energy obtained from the earth(geo). Generally, from the hot rocks present inside the earth. This energy is used to generate electricity. The hot rocks inside the earth convert the water into steam, the hot steam is then piped out and is used to rotate a turbine that activates a generator, which produces electricity.

1) It is a renewable source of energy.
2) By far, it is non-polluting and environment-friendly.
3) The maintenance cost of geothermal power plants is very less.

#### Question 13:

What are trophic levels? Give an example of a food chain having four organisms and name the different trophic levels in it. Draw a sketch to show these trophic levels.

Trophic level of an organism is the position it occupies in a food chain.

Grass (Producer) →Grasshopper (Primary consumer) →Rat (Secondary consumer) →Owl (Tertiary consumer)

#### Question 14:

What are the three R's to save the environment? Explain with examples.

The three R’s that need to be practiced in order to save the environment are:

• Reduce: Reducing the usage of resources will help save them for the future. E.g.: reducing usage of electricity by switching off fans and lights when not in use.

• Recycle: Plastics, paper, and glass can be recycled to make other objects.

• Reuse: Using things again and again. For example, jam bottles made of glass can be used to store salt, sugar, oil, etc.

#### Question 15:

(a) What is a 'gene'? Explain the meaning of dominant genes and recessive genes with examples.

​(b) In humans, if gene B gives brown eyes and gene b gives blue eyes, what will be the colour of the eyes of the persons having the following combinations of genes?
(i) BB (ii) bb (iii) Bb

(a) A gene is a unit of inheritance that is transferred from the parent to the offspring. It controls the expression of a character. The gene which can express its character even when it is present as a single copy is called a dominant gene. Also it is able to express its characters in all the generations.
However, a gene which can express its character, only when it is present in pairs is called a recessive gene.

(b) (i) BB - brown eyes
(ii) bb - blue eyes
(iii) Bb - brow eyes

#### Question 16:

(a) What were the two achievements of Mendeleev's periodic table? What was the basis of classification of elements in it?
(b) An element X (2, 8, 2) combines separately with (NO3), (SO4)2− and (PO4)3− radicals.
(c) To which group of the periodic table does the element 'X' belong? Will it form covalent or ionic compound? Why?
(d) To which period of the periodic table does the element X belong? Give reason for your answer.
(e) Write the name and symbol of element X. Also give the name and symbol of another element which belongs to the same period as element X.

(a) Achievements of the Mendeleev's periodic table are as under: (You can write any two)
(i) The systematic study of elements
(ii) Prediction of new elements
(iii) Correction of atomic mass

Elements were classified on the basis of hydrides and oxides formed by elements.

(b) Element X with electronic configuration is 2, 8 ,2
So the number of valence electrons of X = 2
Number of valence electrons = valency of X
Valency of the nitrate ions (NO3)- = 1, so compound formed with element X and nitrate will be M(NO3)2.
Valency of the sulphate ions (SO4)-2 = 2, so compound formed with element X and sulphate will be MSO4.
Valency of the phosphate ions (PO4)-3 = 3, so compound formed with element X and phosphate will be M3(PO4)2.

(c) The atomic number of element X is 12, valence electrons are 2. Thus, X belongs to the second group of the periodic table.
It will form an ionic bond, to attain noble gas configuration it will easily lose two electrons.

(d) The atomic number of element X is 12, valence electrons are 2. Thus, X belongs to the third period of the periodic table.

(e) The atomic number of element X is 12, which resembles magnesium (Mg) of the periodic table.
Another element which belongs to the same period will be sodium (Na).

#### Question 17:

Four metals A, B, C and D are, in turn, added to the following solutions one by one. The observations made are tabulated below:

 Metal Iron (II) sulphate Copper (II) sulphate Zinc sulphate Silver nitrate A No reaction Displacement - - B Displacement - No reaction - C No reaction No reaction No reaction Displacement D No reaction No reaction No reaction No reaction
Answer the following questions based on above information:
(i) Which is the most active metal and why?
(ii) What would be observed if B is added to a solution of copper (II) sulphate and why?
(iii) Arrange the metals A, B, C and D in order of increasing reactivity.
(iv) Container of which metal can be used to store both zinc sulphate solution and silver nitrate solution. Give reason for your choice.
(v) Which of the above solutions can be easily stored in a computer made up of any of these metals?

When A, B, C, and D are reacted with iron sulphate, then only B will displace iron from iron sulphate. Hence, B is more reactive than iron.
When A, B, C, and D are reacted with copper sulphate, then only A will displace copper from copper sulphate. Hence, A is more reactive than copper.
When A, B, C, and D are reacted with zinc sulphate, then no reaction takes place. Hence, C is less reactive than iron, copper, and zinc.
When A, B, C, and D are reacted with silver nitrate, then only C will displace silver from silver nitrate. Hence, C is more reactive than silver.
D is less reactive than iron, copper, zinc, and silver.

(a) So, from the following results, we can conclude that B is the most reactive metal.

(b) When B is added to the copper sulphate solution then it will displace copper from copper sulphate.

(c) Increasing order of reactivity of A, B, C, and D is:
D < C < A < B.

(d) As D is less reactive from all the metal, so D can be used as a container to store zinc sulphate and silver nitrate solutions.

(e) Zinc sulphate can be easily stored in a container made up of these metals.

#### Question 18:

(a) Two lenses have power of (i) + 2 D (ii) −4 D. What is the nature and focal length of each lens?
​(b) An object is kept at a distance of 100 cm from each of the above lenses. Calculate the (i) image distance (ii) magnification in each of the two cases.

(a) Power of a lens is given by reciprocal of its focal length. i.e.

A negative power means a negative focal length and positive power means positive focal length. As we know, a converging or convex lens has a positive focal length and a diverging or concave lens has a negative focal length. Therefore,
(i) The lens with positive power '+2D' is a converging lens
(ii) The lens with negative power '−4 D' is a diverging lens in nature.

(b) (i) Power of the lens = +2D,

Focal length

Object distance = $-$100 cm

Using the lens formula,

So, the image distance for the first lens is 100 cm.

Magnification of the lens =

(ii) Power of the lens = -4D,

Focal length

Object distance = $-$100 cm

Using the lens formula,

So, the image distance for the second lens is $-$25 cm.

Magnification of the lens =

#### Question 19:

In a household electric circuit different appliances are connected in parallel to one another. Give two reasons.

An electrician puts a fuse of rating 5 A in that part of domestic electrical circuit in which an electric heater of rating 1.5 kW, 220 V is operating. What is likely to happen in this case and why? What change, if any, needs to be made?

In a household electric circuit different appliances are connected in parallel to one another so that:

(i) The appliances can be operated independently.
(ii) They get the same applied voltage.

We know that power,

Now, the current flowing through the circuit will be,

Here, P = 1.5 kW = 1500 W

V = 220 volts

So,

As we can see the current flowing the circuit is more than the maximum current rating of the fuse. This means, that the fuse will blow (or melt) and the circuit will break. Therefore, no current will flow further in the circuit.

#### Question 20:

(a) Draw a neat diagram of human brain. Label medulla and cerebellum on this diagram. Write the functions of these two parts.
​(b) "Both overproduction and underproduction of growth hormone leads to disorders in the body". Explain.

(a)

Function of cerebellum − It helps to maintain posture, equilibrium, and coordination in voluntary movements.

Function of medulla −It helps to control our involuntary muscles such as cardiac, respiratory, etc. It controls the activities of internal organs

(b) Growth hormones are required for the proper development of the body. Oversecretion or undersecretion of this hormone can lead to various types of abnormalities.
The two abnormalities associated with growth hormone are dwarfism and gigantism.
Dwarfism is caused when the growth hormone is not secreted in required amount whereas the over secretion of the growth hormone results in gigantism.

#### Question 21:

(a) Draw a neat diagram of a flower showing its various parts.
(b) What is pollination? How does pollination occur?
(c) Describe the process of fertilisation in a flower with the help of labelled diagrams.
​(d) What changes take place in the flower after fertilisation which lead to the formation of seeds and fruit?

(a)

(b) Pollination is the process in which the transfer of pollen grains takes place from anther to stigma for the purpose of fertilization in plants.

Pollination can occur by two ways -

• Self pollination: When the pollen reaches the stigma of the same flower, the process is known as self pollination.

• Cross pollination: When the pollen reaches the stigma of a different flower on the same plant, or the flower of a different plant of the same kind, the process is known as cross-pollination.

(c) Fertilisation is the process of fusion of male and female gametes. In plants this process is called as double fertilisation. It is a characteristic feature of flowering plants. In this process, out of the two sperm nuclei, one sperm nucleus fuses with the egg nucleus to form an embryo (this process is called syngamy) and another fuses with the polar nucleus to form an endosperm (this process is called triple fusion). Because two kinds of fusion, syngamy and triple fusion, take place, the process is known as double fertilisation.

(d) After the process of fertilisation, the following changes take place.

• The ovary gives rise to the fruit while the other structures of the flower fall down.

• The ovules present inside the ovary develop into seeds. Seeds contain an embryo, which is protected by the seed coat.

#### Question 22:

A student performs an experiment to study the magnetic effect of current around a current carrying straight conductor. He reports that:
(i) the direction of deflection of the north pole of a compass needle kept at a given point near the conductor remains unaffected even when the terminals of the battery sending current in the wire are interchanged.
(ii) for a given battery, the degree of deflection of a N-pole decreases when the compass is kept at a point farther away from the conductor.
Which of the above observations of the student is incorrect and why?

Observation (i) is wrong because the deflection of a compass needle by the current-carrying straight conductor depends upon the magnetic field around it. So, it is the magnetic field produced by the current-carrying conductor which deflects the compass needle. Therefore, if we reverse the direction of current flowing in the conductor then the deflection of the magnetic needle would also be in the opposite direction.

Observation (ii) is correct because magnetic field strength decreases as we move away from the conductor. So, the deflection would decrease too.

#### Question 23:

You are given three resistors of 2 ohms, 4 ohms, and 6 ohms. With the help of these resistors, how can you get a resultant resistance of (i) 12 ohms, and (ii) 3 ohms?

(i) To obtain a resultant resistance of 12-ohms, we can directly connect all the resistances in series. The net resistance of the series combination is simply the sum of all the resistances. Which is, in this case, would be 12-ohms.

(ii) To get a resultant resistance of 3-ohms, we can connect 2-ohm and 4-ohm resistors in series and then we can connect that series combination in parallel with 6-ohm resistor. By doing this, we can get a total of 3-ohm resistance, because the net resistance in series would be 6-ohms and then net resistance of the parallel combination of two 6-ohm resistors would be 3-ohms.

#### Question 24:

A student is performing displacement reactions of metals with salt solutions.
(a) In first case, the student keeps a strip of copper metal in iron (II) sulphate solution for a considerable time
(b) In second case, the student keeps a strip of zinc metal in copper (II) sulphate solution for a considerable time
(i) In which case the displacement reaction will take place? Why?
​(ii) In which case the displacement reaction will not take place? Why not?

(i) When a student keeps a strip of zinc metal in copper sulphate, displacement reaction will take place. Zinc is more reactive than copper sulphate, so zinc will displace copper from copper sulphate and form zinc sulphate.

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

(ii) When a student keeps a strip of copper metal in iron sulphate, no reaction will take place. Copper is less reactive than iron so it will not be able to displace iron from iron sulphate.

#### Question 25:

An organic compound C2H4O2 is taken in a test-tube and a pinch of baking soda is added to it. A gas is evolved which turns lime water milky.
(a) Name the gas evolved.
(b) Name the functional group present in the organic compound.
​(c) Write the name and formula of the organic compound.

(a) The reaction of C2H4O2 with baking soda will produce carbon dioxide gas which turns lime water milky.

${\mathrm{CH}}_{3}\mathrm{COOH}+{\mathrm{NaHCO}}_{3}\to {\mathrm{CH}}_{3}\mathrm{COONa}+{\mathrm{CO}}_{2}+{\mathrm{H}}_{2}\mathrm{O}$

(b) The functional group present in the organic compound will be carboxylic acid (COOH).

(c) The name of the molecule will be ethanoic acid and the molecular formula of organic compound will be CH3COOH.

#### Question 26:

What does the given experimental set-up demonstrate?

​Use scientific terms to describe the phenomenon.

The above experimental setup is used to determine the response of plant parts towards sunlight. The bending of shoot in the direction of sunlight is termed as phototropism.

#### Question 27:

A student first keeps a potted plant having green leaves in a dark room for more than 3 days. He then takes out this potted plant from the dark room and places it in bright sunshine for about 3 days.
(a) Which substance present in the green leaves is all used up when the potted plant is kept in a dark room?
(b) What is this process known as?
(c) Which plant process uses up all the above substance from green leaves when the potted plant is kept in the dark room?
(d) Which process does not take place in the green leaves of the plant when it is kept in the dark room?