31/4/1 2020 Class 10 Science Question Paper Solution
SCIENCE
SECTION A
1) Write the number of valence electrons present in a nitrogen atom ( 147N).
Ans: 5 valence electrons.
2) Define the term induced electric current.
Ans: The electric current generated /induced in a conductor by changing magnetic field around it.
3) Answer question numbers 3(a) – 3(d) on the basis of your understanding of the following paragraph and the related studied concepts :
Around the year 1800, only 30 elements were known. Dobereiner in 1817 and Newlands in 1866 tried to arrange the then known elements and framed laws which were rejected by the scientists. Even after the rejection of the proposed laws, many scientists continued to search for a pattern that correlated the properties of elements with their atomic masses.
The main credit for classifying elements goes to Mendeleev for his most important contribution to the early development of a Periodic table of elements wherein he arranged the elements on the basis of their fundamental property, the atomic mass and also on the similarity of chemical properties. The formulae of their hydrides and oxides were treated as basic criteria for the classification of the elements.
However, Mendeleev’s classification also had some limitations as it could not assign the position to isotopes. He also left some gaps in the periodic table.
3(a) State Mendeleev’s Periodic Law.
Ans: The properties of elements are the periodic functions of their atomic masses.
3(b) Why did Mendeleev leave some gaps in the Periodic table ?
Ans: To fill with undiscovered elements.
3(c) If the letter ‘R’ was used to represent any of the elements in the group, then the hydride and oxide of carbon would respectively be represented as
(i) RH4 , RO
(ii) RH4 , RO2
(iii) RH2 , RO2
(iv) RH2 , RO
Ans: (ii)/RH4, RO2
3(d) Isotopes are
(i) Atoms of an element with similar chemical properties but different atomic masses.
(ii) Atoms of different elements with similar chemical properties but different atomic masses.
(iii) Atoms of an element with different chemical properties but same atomic masses.
(iv) Atoms of different elements with different chemical properties but same atomic masses.
Ans: (i)/Atoms of an element with similar chemical properties but different atomic masses.
4) Answer question numbers 4(a) – 4(d) on the basis of your understanding of the following paragraph and the related studied concepts :
India today is facing the problem of overuse of resources, contamination of water and soil and lack of methods of processing the waste. The time has come for the world to say goodbye to ‘‘single-use plastics’’. Steps must be undertaken to develop environment-friendly substitutes, effective plastic waste collection and methods of its disposal.
Indore treated 15 lakh metric tonnes of waste in just 3 years, through biomining and bioremediation techniques. Bioremediation involves introducing microbes into a landfill to naturally ‘break’ it down and biomining involves using trommel machines to sift through the waste to separate the ‘soil’ and the waste component. The city managed to chip away 15 lakh metric tonnes of waste at a cost of around ₹ 10 crore. A similar experiment was successfully carried out in Ahmedabad also.
4(a) State two methods of effective plastic waste collection in your school.
Ans: Use of separate bins for plastic and paper ; separation of biodegradable and non biodegradable wasteor any other.
4(b) Name any two uses of ‘‘single-use plastic’’ in daily life.
Ans:
- Packaging of articles like water, food, milk, biscuits etc.
- Disposable utility items –bowls, tumblers, plates , leaves etc.
4(c) If we discontinue the use of plastic, how can an environment-friendly substitute be provided ?
Ans: By providing cloth /jute /earthern pots and utensils/ paper or any other material for the similar purposes.
4(d) Do you think microbes will work similarly in landfill sites as they work in the laboratory ? Justify your answer.
Ans:
- Yes
- The action of microbes is tested in the laboratory creating the same conditions as in the landfill.
5) Which one of the following statements is correct about the human circulatory system ?
(A) Blood transports only oxygen and not carbon dioxide.
(B) Human heart has five chambers.
(C) Valves ensure that the blood does not flow backwards.
(D) Both oxygen-rich and oxygen-deficient blood gets mixed in the heart.
Ans: (C) / Valves ensure that the blood does not flow backwards.
6) Anaerobic process
(A) takes place in yeast during fermentation.
(B) takes place in the presence of oxygen.
(C) produces only energy in the muscles of human beings.
(D) produces ethanol, oxygen and energy.
Ans: (A)/ takes place in yeast during fermentation.
OR
Most of the digestion and absorption of the food takes place in the
(A) small intestine.
(B) liver.
(C) stomach.
(D) large intestine.
Ans: (A)/ small intestine
7) Fertilisation is the process of
(A) transfer of male gamete to female gamete.
(B) fusion of nuclei of male and female gamete.
(C) adhesion of male and female reproductive organs.
(D) the formation of gametes by a reproductive organ.
Ans: (B) /fusion of nuclei of male and female gamete.
8) If a person has five resistors each of value 1/5 Ω, then the maximum resistance he can obtain by connecting them is
(A) 1 Ω
(B) 5 Ω
(C) 10 Ω
(D) 25 Ω
Ans: (A) 1 Ω
OR
The resistance of a resistor is reduced to half of its initial value. In doing so, if other parameters of the circuit remain unchanged, the heating effects in the resistor will become
(A) two times.
(B) half.
(C) one-fourth.
(D) four times.
Ans: (B) /half
9) Fleming’s Right-hand rule gives
(A) magnitude of the induced current.
(B) magnitude of the magnetic field.
(C) direction of the induced current.
(D) both, direction and magnitude of the induced current.
Ans: (B)/ The nucleus of Uranium is bombarded with high energy neutrons.
10) Which one of the following statements is not true about nuclear energy generation in a nuclear reactor ?
(A) Energy is obtained by a process called nuclear fission.
(B) The nucleus of Uranium is bombarded with high energy neutrons.
(C) A chain reaction is set in the process.
(D) In this process a tremendous amount of energy is released at a controlled rate.
Ans: (B) / The nucleus of Uranium is bombarded with high energy neutrons.
OR
The biggest source of energy on Earth’s surface is
(A) Biomass
(B) Solar radiations
(C) Tides
(D) Winds
Ans: Biomass
11) Food web is constituted by
(A) relationship between the organisms and the environment.
(B) relationship between plants and animals.
(C) various interlinked food chains in an ecosystem.
(D) relationship between animals and environment.
Ans: (C) /various interlinked food chains in an ecosystem.
12) Choose the incorrect statement from the following :
(A) Ozone is a molecule formed by three atoms of oxygen.
(B) Ozone shields the surface of the Earth from ultraviolet radiations.
(C) Ozone is deadly poisonous.
(D) Ozone gets decomposed by UV radiations.
Ans: Treat all answers as correct.
13) Assertion (A) : Following is a balanced chemical equation for the action of steam on iron : 3Fe + 4H2O-> Fe3O4 + 4H2
Reason (R) : The law of conservation of mass holds good for a chemical equation.
Ans: (b) /Both (A) and (R) are true but (R) is not the correct explanation of theassertion (A).
14) Assertion (A) : The sex of a child in human beings will be determined by the type of chromosome he/she inherits from the father.
Reason (R) : A child who inherits ‘X’ chromosome from his father would be a girl (XX), while a child who inherits a ‘Y’ chromosome from the father would be a boy (XY).
Ans: (a) /Both (A) and (R) are true and ( R) is the correct explanation of the assertion (A).
SECTION B
15) Lead nitrate solution is added to a test tube containing potassium iodide solution.
(a) Write the name and colour of the compound precipitated.
Ans: Lead iodide; Yellowcolour
(b) Write the balanced chemical equation for the reaction involved.
Ans: Pb(NO3)2 + 2 KI -> PbI2 + 2KN03
(c) Name the type of this reaction justifying your answer.
Ans: Double displacement reaction ; Due to exchange of ions.
OR
What happens when food materials containing fats and oils are left for a long time ? List two observable changes and suggest three ways by which this phenomenon can be prevented.
Ans:
- Fats and oils become rancid.
- Observable changes –
1.) Change in taste
2.) Change in smell
- Three ways of prevention :-
i) Addition of antioxidants / substance which prevent oxidation.
ii) Keeping food in air tight containers.
iii) Use of nitrogen gas in packaged food.
16) List three differentiating features between the processes of galvanisation and alloying.
Ans:
Galvanisation |
Alloying |
1.) Coating a layer of zinc metal on the metal. |
1.) Mixing of a metal with metal or non-metal. |
2.) Not a homogeneous mixture. |
2.) Homogeneous mixture. |
3.) No change in physical properties of metals takes place. |
3.)Change in physical properties of metals takes place. |
4.) The process is an outcome of the reactivity of metals. |
4.) Reactivity of metals do not play any role in it. |
5.) Prevents rusting only. |
5.) Some alloys may prevent rusting and also used for other advantages. |
OR
Compare in tabular form the reactivities of the following metals with cold and hot water :
(a) Sodium
(b) Calcium
(c) Magnesium
Ans:
Cold Water |
Hot Water |
|
Sodium |
Reacts violently Heat is evolved. |
React more violently More heat is evolved. |
Calcium | Reacts less violently as compared to sodium. | Reacts violently with hot water and sticks to surface of metal and floats on surface of water. |
Magnesium | Does not react with cold water | · React with hot water and floats on surface of water. |
17) Carbon, a member of group 14, forms a large number of carbon compounds estimated to be about three million. Why is this property not exhibited by other elements of this group ? Explain.
Ans:
- Carbon atom, the first member of group 14 has the smallest size in the group and highest inter-atomic force of attraction.
- It has four valence electrons and requires four more electrons to attain stable configuration.
- Due to its small size, nucleus of carbon is able to hold the shared pairs of electrons strongly.
- The bonds formed by other elements of the same group are weaker due to bigger size of their atoms.
18) A cheetah, on seeing a prey, moves towards him at a very high speed. What causes the movement of his muscles ? How does the chemistry of cellular components of muscles change during this event ?
Ans:
- A cheetah on seeing a prey generates a nerve impulse which reaches the muscles and the muscle fibre moves. The muscle cell will then move by changing their shape so that muscle cells shorten.
- Muscle cells have special proteins that change both shape and their arrangement in the cell in response to nervous electrical impulses. When this happens new arrangements of these proteins give the muscle cells a shorter form.
19) Define geotropism. Draw a labelled diagram of a plant showing geotropic movements of its parts.
Ans: The movement of the growth of the roots downwards and the shoots upwards under the stimuli of gravity is called geotropism./ The movement of the part of the plant towards or away from the stimulus gravity.
20) Define the term evolution. ‘‘Evolution cannot be equated with progress.’’ Justify this statement.
Ans:
- Evolution – Gradual change in living organisms with time since the beginning of life resulting in the formation of a new species/ Evolution is simply the generation of diversity and the shaping of diversity by environmental selection.
- Evolution cannot be equated with progress because more and more complex body designs have emerged and evolved over time but this does not mean that older designs are inefficient.Foreg. Bacteria are simpler organisms but some inhabit the most inhospitable habitats like hot springs, deep sea, thermal vents and the ice in Antartica.
OR
‘‘During the course of evolution, organs or features may be adapted for new functions.’’ Explain this fact by choosing an appropriate example.
Ans: Examples of feathers :
– Feathers can start out as providing insulation in cold weather but later they might become useful for flight.
– Some dinosaurs have feathers but they could not fly.
– Birds later adapted the feathers for flight .
– This shows that birds are closely related to reptiles.
21) A concave mirror is used for image formation for different positions of an object. What inferences can be drawn about the following when an object is placed at a distance of 10 cm from the pole of a concave mirror of focal length 15 cm ?
(a) Position of the image
Ans: Behind the mirror.
(b) Size of the image
Ans: Magnified.
(c) Nature of the image Draw a labelled ray diagram to justify your inferences.
Ans: Virtual and erect.
22) The refractive index of a medium ‘x’ with respect to a medium ‘y’ is 2/3 and the refractive index of medium ‘y’ with respect to medium ‘z’ is 4/3. Find the refractive index of medium ‘z’ with respect to medium ‘x’. If the speed of light in medium ‘x’ is 3 × 108 ms-1, calculate the speed of light in medium ‘y’.
Ans:
- nxy = 2 /3
∴nyx = 3 /2
nyz = 4 /3
∴nzy = 3/ 4
nzx = nzy X nyx
∴ nzx = 3/ 4 X 3/ 2 = 9 /8
- nyx = Vx /Vy
3/ 2 = 3 X 10 8 /Vy
Vy = 3 X 10 8 X 2/ 3 = 2 X 10 8 m/s
23) A person may suffer from both myopia and hypermetropia defects.
(a) What is this condition called ?
Ans: Presbyopia
(b) When does it happen ?
Ans: Gradual weakening of the ciliary muscles of the eye/ diminishing flexibility of the eye lens.
(c) Name the type of lens often required by the persons suffering from this defect. Draw labelled diagram of such lenses.
Ans: Bifocal lens
24) How will you use two identical glass prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light ? Draw and label the ray diagram.
Ans: By placing second (identical) prism in an inverted position with respect to the first prism.
SECTION C
25) A cloth strip dipped in onion juice is used for testing a liquid ‘X’. The liquid ‘X’ changes its odour. Which type of an indicator is onion juice ? The liquid ‘X’ turns blue litmus red. List the observations the liquid ‘X’ will show on reacting with the following :
(a) Zinc granules
Ans: Colourless and Odourless gas is evolved with bubbles .
Zinc + Acid -> Zinc Salt + H2 ↑
(b) Solid sodium carbonate Write the chemical equations for the reactions involved.
Ans: Brisk effervescence/ colourless and odourless gas is evolved.
Sodium carbonate + Acid ->Sodium salt of Acid + Water + Carbon dioxide↑
( or by using any example of acid like HCl/ H2SO4)
OR
Define water of crystallisation. Give the chemical formula for two compounds as examples. How can it be proved that the water of crystallisation makes a difference in the state and colour of the compounds ?
Ans:
- Water of crystallization is the fixed number of water molecules present in one formula unit of a salt.
- Examples CuSO4 .5H2O
Na2CO3.10 H2O
- Heat a few crystals of hydrated copper sulphate( bluecolour) in a dry boiling tube. Water droplets are seen in the boiling tube.
Colour : The colour of copper sulphate changes to white .
State : The blue crystal changes to white powder.
26) (a) (i) Write two properties of gold which make it the most suitable metal for ornaments.
Ans: (i) Ductility / Malleability / Lusture.
(ii) Name two metals which are the best conductors of heat.
Ans: Silver , Copper
(iii) Name two metals which melt when you keep them on your palm.
Ans: Gallium, Caesium
(b) Explain the formation of ionic compound CaO with electron-dot structure. Atomic numbers of calcium and oxygen are 20 and 8 respectively.
Ans:
27) (a) Why is nutrition necessary for the human body ?
Ans: For providing energy for various metabolic processes / Formation of new cells / Repair of damaged or worn out cells & tissues / Developing resistance against diseases.
(b) What causes movement of food inside the alimentary canal ?
Ans: Peristaltic movement / Peristalsis/ Rhythmic contraction and relaxation of the muscles in the lining of alimentary canal.
(c) Why is small intestine in herbivores longer than in carnivores ?
Ans: Herbivores eat plant matter which is rich in cellulose and takes longer time to digest and hence longer small intestine.
(d) What will happen if mucus is not secreted by the gastric glands ?
Ans: The inner lining of the stomach will not be protected from the action of the acid /HCl
28) Draw a neat diagram showing fertilisation in a flower and label
(a) Pollen tube,
(b) Male germ cell and
(c) Female germ cell, on it. Explain the process of fertilisation in a flower. What happens to the (i) ovary and (ii) ovule after fertilisation ?
Ans:
- Process of fertilization : Pollen tube is formed from the pollen grain. Fusion of male germ cell with female germ cell to form zygote.
- Ovary- Changes into fruit
- Ovule- Changes into Seed
OR
(a) What is puberty ?
Ans: The period during adolescence is called puberty/age of males and females at which reproductive organs become functional.
(b) Describe in brief the functions of the following parts in the human male reproductive system :
(i) Testes
Ans: Testes – Production of sperms /Secretion of male sex hormone testosterone.
(ii) Seminal vesicle
Ans: Seminal vesicle – secretes a fluid which makes the transport of sperms easier/ the fluid secreted gives nutrition to sperms.
(iii) Vas deferens
Ans: Vas deferens- carries the sperms to the seminal vesicle.
(iv) Urethra
Ans: Urethra- forms a common passage for both the sperms and urine.
(c) Why are testes located outside the abdominal cavity ?
Ans: Because the sperm formation requires a lower temperature than the normal body temperature.
(d) State how sperms move towards the female germ cell.
Ans: With the help of a long tail.
29) Draw a schematic diagram of a circuit consisting of a battery of 3 cells of 2 V each, a combination of three resistors of 10 Ω, 20 Ω and 30 Ω connected in parallel, a plug key and an ammeter, all connected in series. Use this circuit to find the value of the following :
Ans:
(a) Current through each resistor
Ans: 11=v/R1=6/10=0.6A
12=V/R2=6/20=0.3A
13=V/R3=6/30=0.2A
(b) Total current in the circuit
Ans: I= I1 + I2 + I3 = 1.1 A
(c) Total effective resistance of the circuit
Ans: Reff = V/ I
= 6 /1.1 = 5.4Ω
OR
Two identical resistors, each of resistance 15 Ω, are connected in
Ans: R1 = R2 = 15Ω V= 6V
(i) series,
Ans: In series :
Rs = R1 + R2 = 15Ω + 15Ω = 30Ω
I = V R3 = 6V /30Ω = 0.2 A
∴ P1 = VI = 6V × 0.2 A = 1.2 Ω
and
(ii) parallel, in turn to a battery of 6 V. Calculate the ratio of the power consumed in the combination of resistors in each case.
Ans: In parallel
Rp = R1 × R2 /R1 + R2 = 15 × 15/ 15 + 15 = 225/ 30 = 7.5Ω
I = V Rp = 6V /7.5Ω = 0.8 A
P2 = VI = 6V × 0.8 A = 4.8Ω
Ratio of power = P1/ P2 = 1.2Ω/ 4.8Ω = 1 /4
∴ P1 ∶ P2 = 1 ∶4
30) (a) State Fleming’s Left-hand rule.
Ans: Flemings’ Left hand rule: Stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the forefinger points in the direction of magnetic field, middle finger in the direction of current , then the thumb will point in the direction of motion or force acting on the conductor.
(b) List three characteristic features of the electric current used in our homes.
Ans: Three characterstic features :
- Reverses direction periodically.
- Frequency of 50 Hz.
- Potential difference between live wire and netural wire is about 220V.
(c) What is a fuse ? Why is it called a safety device ?
Ans:
- Fuse is a safety device used in a circuit (or appliance) to prevent damage due to overloading/ short circuiting.
- It protects the circuit ( or appliance) by stopping the flow of any unduly high electric current / If current larger than the specified valueflows through the circuit , due to Joule’s heating effect the fuse wire melts and breaks the circuit.
(d) Why is it necessary to earth metallic electric appliances ?
Ans: It provides a low resistance conducting path for the current and protects the user from electric shock due to leakage of current.
CBSE Class 10 Previous Question Paper 2020 Solution
- Science (Set No 31/1/1)
- Science (Set No 31/1/2)
- Science (Set No 31/1/3)
- Science (Set No 31/2/1)
- Science (Set No 31/2/2)
- Science (Set No 31/2/3)
- Science (Set No 31/3/1)
- Science (Set No 31/3/2)
- Science (Set No 31/3/3)
- Science (Set No 31/4/1)
- Science (Set No 31/4/2)
- Science (Set No 31/4/3)
- Science (Set No 31/5/1)
- Science (Set No 31/5/2)
- Science (Set No 31/5/3)