31/ 1/3 2020 Class 10 Science Question Paper Solution
Section – A
(1) Name a cyclic understand carbon compound.
Ans: Cyclopentene / Cyclohexene-formula or structure (or any other).
(2) State an important advantage of using alternating current (a.c) over direct current(d.c).
Ans: In case of AC – Electric power can be transmitted over long distances without much loss of energy.
(3) The growing size of the human population is a cause of concern for all people. The rate of birth and death in a given population will determine its size. Reproduction is the process by which organism increase their population. The process of sexual maturation for reproduction is gradual and takes place while general body growth is still going on. Some degree of sexual maturation does not necessarily mean that mind or body is ready for sexual acts or for having and bringing up children. Various contraceptive devices are being used by human beings to control the size of population. devices are being used by human beings to control the size of population.
(a) List two common signs of sexual maturation in boys and girls.
Ans: Thick hair growth in armpits, genital area/thinner hair on arms, legs, face/ more active oil secretion from glands on skin/Occurrence of pimples
(b) What is the result of reckless female foeticide?
Ans: Imbalance in male – female ratio/ decline in child sex ratio
(c) Which contraceptive method changes the hormonal balance of the body?
Ans: Oral pills
(d) Write two factors that determine the size of a population.
Ans: Rate of birth and death
(4) Human body is made up of five important components, of which water is the main component. Food as well as potable water are essential for every human being. The food is obtained from plants through agriculture. Pesticides are being used extensively for a high yield in the fields. These pesticides are absorbed by the plants from the soil along with water and minerals and from the water bodies these pesticides are taken up by the aquatic animal and plants. As these chemicals are not biodegradable, they get accumulated progressively at each trophic level. The maximum concentration of these chemicals gets accumulated in our bodies and greatly affects the health of our mind and body.
(a) Why is the maximum concentration of pesticides found in human beings?
Ans: Human beings are at the top level in any food chain
(b) Give one method which could be applied to reduce our intake of pesticides through food to some extent.
Ans: Washing of vegetables, fruits, grains thoroughly/Organic farming/ Use of bio pesticides
(c) Various steps in a food chain represent:
(a) Food web
(b) Trophic level
(c) Ecosystem
(d) Biomagnification
Ans: (b) / Trophic level
(d) With regard to various food chains operating in an ecosystem, man is a:
(a) Consumer
(b) Producer
(c) Producer and consumer
(d) Producer and decomposer
Ans: (a) / Consumer
(5) Which one of the following is responsible for the sustenance of underground water?
(a) Loss of vegetation cover
(b) Diversion for high water demanding crops
(c) Pollution from urban wastes
(d) Afforestation
Ans: Afforestation
(6) Incomplete combustion of coal and petroleum:
(a) increases air pollution.
(b) increases efficiency of machines.
(c) reduces global warming
(d) produce poisonous gases.
Ans: (b)
The correct option is:
(a) (A) and (B)
(b) (A) and (D)
(c) (B) and (C)
(d) (C) and (D)
Ans: (A) and (D)
(7) When sodium hydrogen carbonate is added to ethanoic acid a gas evolves. Consider the following statements about the gas evolved?
(a) It turns lime water milky.
(b) It is evolved with a brisk effervescence.
(c) It has a smell of burning sulphur.
(d) It is also a by – product of respiration.
Ans: (d)
The correct statements are:
(a) (A) and (B) only
(b) (B) and (D) only
(c) (A), (C) and (D)
(d) (A), (B) and (D)
Ans: (A) ( B ) and ( D )
(8) When a small amount of acid is added to water, the phenomena which occur are:
(a) Dilution
(b) Neutralisation
(c) Formation of H3O+ ions
(d) Salt formation
Ans: (a)
The correct statements are:
(a) (A) and (C)
(b) (B) and (D)
(c) (A) and (B)
(d) (C) and (D)
Ans: ( A ) and ( C )
(9) A real image is formed by the light rays after reflection or refraction when they:
(a) actually meet or intersect with each other.
(b) actually converge at a point.
(c) appear to meet when they are produced in the backward direction.
(d) appear to diverge from a point.
Ans: (c)
Which of the above statements are correct?
(a) (A) and (D)
(b) (B) and (D)
(c) (A) and (B)
(d) (B) and (C)
Ans: ( A ) and ( B )
Or
Consider the following properties of virtual images:
(a) cannot be projected on the screen
(b) are formed by both concave and convex lens
(c) are always erect
(d) are always inverted
Ans: (c)
The correct properties are:
(a) (A) and (D)
(b) (A) and (B)
(c) (A), (B) and (C)
(d) (A), (B) and (D)
Ans: ( A ) and ( B )
(10) At the time of short circuit, the electric current in the circuit:
(a) vary continuously
(b) does not change
(c) reduces substantially
(d) increases heavily
Ans: Increases heavily
Or
Two bulbs of 100 W and 40 W are connected in series. The current through the 100 W bulb is 1 A. The current through the 40 W bulb will be:
(a) 0.4 A
(b) 0.6 A
(c) 0.8 A
(d) 1 A
Ans: 1 A
(11) Calcium oxide reacts vigorously with water to produce slaked lime.
CaO(s) + H2O(I) → Ca(OH)2(aq)
This reaction can be classified as:
(a) Combination reaction
(b) Exothermic reaction
(c) Endothermic reaction
(d) Oxidation reaction
Ans: (d)
Which of the following is a correct option?
(a) (A) and (C)
(b) (C) and (D)
(c) (A), (C) and (D)
(d) (A) and (B)
Ans: (A) and (B)
Or
When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid so formed remains in the solution. The reaction is an example of a:
(a) Combination reaction
(b) Displacement reaction
(c) Decomposition reaction
(d) Double displacement reaction
Ans: Double displacement reaction
(12) In a double displacement reaction such as the reaction between sodium sulphate solution and barium chloride solution:
(a) exchange of atoms takes place
(b) exchange of ions takes place
(c) a precipitate is produced
(d) an insoluble is produced
Ans: (d)
The correct option is:
(a) (B) and (D)
(b) (A) and (C)
(c) only (B)
(d) (B), (C) and (D)
Ans: (d) / (B), (C) and (D)
(13) Assertion (A): Esterification is a process in which a sweet smelling substance is produced.
Reason (R): When esters react with sodium hydroxide an alcohol and sodium salt of carboxylic acid are obtained.
Ans: (b) / Both (A) and (R) are true but (R) is not the correct explanation of the assertion (A).
(14) Assertion (A): A solar cooker cooks the meal due to green house effect.
Reason (R): The plane mirror is responsible for producing the green house effect.
Ans: (c)/ A is true but R is false
SECTION – B
(15) (a) Write the mathematical expression for Joule’s law of heating.
Ans: (i)H = I2Rt
(b) Compute the heat generated while transferring 96000 coulomb of charge in two hours through a potential difference of 40 V.
Ans: (ii) H = V.I.t
= V.Q
Given : V = 40 volts , Q = 96000 C
H = 40 V × 96000 C
= 3.84 × 106 J
(16) Draw a labelled diagram to show (i) reddish appearance of the sun at the sunrise or the sunset an (ii) white appearance of the sun at noon when it is overhead.
Ans:
(17) (a) Draw the structures for (i) ethanol, (ii) ethanoic acid.
Ans: (i) Ethanol-C2H5OH/CH3CH2OH/
(ii) Ethanoic Acid – CH3COOH/
(b) Why is the conversion of ethanol to ethanoic acid considered an oxidation reaction? Write the oxidising agent used in the reaction involved.
Ans: As oxygen is added to ethanol
Oxidizing agent – Alkaline KMnO4 or
Acidified K2Cr2O7
(18) Name the parts (a) to (e) in the following diagram.
Ans: a – receptor/ skin
b – sensory neuron
c – spinal cord
d – relay neuron e – motor neuron
What is the term given to the sequence of events occurring in the diagram?
Ans:
- Reflex Arc
Or
(a) What is tropism?
Ans: Directional movements of the plant part towards or away from the stimulus.
(b) How do auxins promote the growth of a tendril around a support?
Ans: When the tip of the tendril comes in contact with the support, more auxin is diffused from the tip towards the side of the tendril away from the support. As a result, that side grows faster and causes the tendril to bend around the support
(19) Why is Tyndall effect shown by colloidal particles? State four instances of observing the Tyndall effect.
Ans: Because of scattering of light. Instances:
- When a fine beam of light enters a smoke-filled dark room through a small hole.
- When sunlight passes through a canopy of dense forest in foggy/ misty conditions.
- Blue colour of sky.
- Red colour of the sun during sunrise or sunset.
Or
Differentiate between a glass slab and a glass prism. What happen when a narrow beam of (i) a monochromatic light, and (ii) white light passes through (a) glass slab and (b) glass prism?
Ans: • Prism has 2 inclined refracting surfaces whereas a glass slab has 2 parallel refracting surfaces.
(i) When monochromatic light passes through a glass slab it gets displaced laterally whereas in prism it gets angularly displaced.
(ii) When white light passes through a glass slab, it gets laterally displaced whereas in prism, dispersion takes place.
(20) Define the term pollination. Differentiate between self pollination and cross pollination. What is the significance of pollination?
Ans:
- Pollination is transfer of pollen from anther to stigma
Self Pollination | Cross Pollination |
Transfer of pollen in the same flower | Transfer of pollen from one flower to another. |
- Pollination leads to fertilization resulting in the formation of zygote.
(21) List the important products of the Chlor – alkali process. Write one important use of each.
Ans: Products: Hydrogen, Chlorine , Sodium hydroxide
Uses:
Hydrogen: In the production of margarine/ ammonia/as a fuel
Chlorine: Water treatment/ swimming pools/ production of PVC/ Disinfectants/CFCs/Pesticides.
Sodium hydroxide: For degreasing metal surfaces/ in making soaps and detergents/ paper making/ artificial fibres.
Or
How is washing soda prepared from sodium carbonate? Give its chemical equation. State the type of this salt. Name the type of hardness of water which can be removed by it?
Ans:
- By recrystallisation of sodium carbonate
- Na2CO3 + 10H2O →Na2CO3.10H2O
- Basic Salt
- Permanent hardness
(22) 1 g of copper powder was taken in a China dish and heated. What change takes place on heating? When hydrogen gas is passed over this heated substance, a visible change is seen in it. Give the chemical equations of reactions, the name and the color of the products formed in each case.
Ans:
- A black colour is formed on the surface
- Original/brown colour is restored.
(23) The near point of the eye of a person is 50 cm. Find the nature and power of the corrective lens required by the person to enable him to see clearly the objects placed at 25 cm. from the eye.
Ans: Near point of Hypermetropia eye = 50 cm
Book placed at, u = -25 cm
Convex lens/converging lens
It will form a virtual image of the abject at near point of defective eye
v = -50 cm
Lens formula
1/f = 1/v – 1/u
1/f = 1/(-50) – 1/(-25)
= 1/50
f = 50cm or 0.50cm
p = 1/f = 1/0.5 = +2D
(24) What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor. Justify your answer.
Ans:
- Homologous structures are those which have similar basic structure and origin but perform different functions.
- Example: forelimbs of reptiles, amphibians, humans, wings of birds
- Yes
- Similarity in basic design of the structure indicates that their ancestors were common.
SECTION – C
(25) Draw a ray diagram in each of the following cases to show the formation of image, when the object is placed:
(i) between optical centre and principal focus of a convex lens.
(ii) anywhere in front of a concave lens.
(iii) At 2F of a convex lens.
State the signs and values of magnifications in the above mentioned cases (i) and (ii)
Ans: In case (i) sign is positive and m> 1
(ii) sign is positive and m < 1
Or
An object 4.0 cm in size, is placed 25.0 cm in front of a concave mirror of focal length 15.0 cm.
Ans: Given h = + 4.0 cm, u = -25.0 cm, f = -15.0 cm
(i) At what distance from the mirror should a screen be placed in order to obtain a sharp image?
Ans: image distance v = ? ; mirror formula : 1/v + 1/u = 1/f
Or 1/v = 1/f – 1/u; = -1/15 – (-1/25)
= 1/15 + 1/25 = -5 +3/75
= -2/75
V = -37.5 cm
The screen should be placed 37.5 cm in front of the mirror.
(ii) Find the size of the image.
Ans: m = h1/h = v/u
ℎ 1 = – / . h
= (-37.5 x 4)/-25
ℎ 1 = – 6.0 cm (size of the image).
(iii) Draw a ray diagram to show the formation of image in this case.
Ans:
Note: Deduct half mark for not showing arrows in ray diagrams.
(26) (a) What is the law of dominance of trains? Explain with an example.
Ans: (a) Law of dominance of traits: -In a cross between a pair of contrasting characters, only one parental character will be expressed in F1 generation which is called dominant trait and the other is called recessive trait.
For example – in pea plants,
All plants in F1 generation were tall proving that the gene for tallness is dominant over the gene for dwarfness/ short, which is not able to express itself in the presence of dominant trait.
(b) Why are the traits acquired during the life time of an individual not inherited? Explain.
Ans: Traits acquired by an organism during its lifetime are known as acquired traits.
These traits are not inherited because they occur in somatic cells only/do not cause any change in the DNA of the germ cells.
(27) (a) A gas released during photosynthesis. Name the gas and also state the way by which the gas is evolved.
Ans: Oxygen
- Released by splitting of water molecules
(b) What are stomata? What governs the opening and closing of stomata?
Ans:
- Tiny pores present on the surface of leaves.
- Opening and closing of stomata is a function of guard cells
- Guard cells swell up, when water flows into them, causing the stomatal pore to open. If the guard cells shrink the pore closes.
Or
(a) Draw a diagram of human alimentary canal an label – gall bladder, pancreas, liver and small intestine on it.
Ans:
(b) Give two reasons to explain why absorption of digested food occurs mainly in the small intestine.
Ans:
- Digestion of flood is completed in small intestine only.
- Finger like projections (villi) in the wall of small intestine provides large surface area for maximum absorption.
- Villi of small intestine are richly supplied with blood vessels for carrying absorbed food to different parts of the body.
(28) Carbon cannot reduce the oxides of sodium, magnesium and aluminium to their respective metals. Why? Wherein the reactivity series these metals are placed? How are these metals obtained from their ores? Take an example to explain the process of extraction along with chemical equations.
Ans:
- These metals have more affinity for oxygen than carbon.
- Towards the top of the reactivity series.
- By electrolytic reduction of their molten ores.
- Example: Extraction of sodium from molten sodium chloride by electrolysis. Process:
- Molten NaCl is taken in an electrolytic cell and on passing electricity Na is deposited at cathode and chlorine is liberated at anode.
Reactions –
At cathode – Na+ + e- → Na
At anode – 2Cl- → Cl2 + 2e–
(29) The position of certain elements in the Modern Periodic Table are shown below.
Using the above table answer the following questions giving reasons in each case:
(i) Which element will form only covalent compounds?
(ii) Which element is a non – metal with valency 2?
(iii) Which element is a metal with valency 2?
(iv) Out of H, C and F which has largest atomic size?
(v) To which family does H, C and F belong?
Ans: (i) E, it has 4 valence electrons .
(ii) B, it needs only 2 electrons to attain stable configuration.
(iii) D , it loses two electrons to attain stable configuration.
(iv) F, it has the largest size since size increases down the group.
(v) Noble gases, outermost shell is complete.
Or
Define atomic size, Give its unit of measurement. In the modern periodic table what trend is observed in the atomic radius in a group and a period and why is it so?
Ans:
- Atomic size is the distance between the centre of the nucleus and the outermost shell of an isolated atom.
- Picometer /pm
- Trends in Atomic radius
In a group: increases down the group ;
due to addition of a new shell .
In a period: atomic radius decreases from left to right ; due to increase in pulling power of nucleus / due to addition of electrons in the same shell.
(30) (a) Explain with the help of the pattern of magnetic field lines the distribution of magnetic field due to a current carrying a circular loop.
Ans:
At Every point of a current carrying circular loop, the concentric circles represent magnetic field around it which become larger as we move away from the wire.
At the center of the loop, these lines appear as straight lines.
(b) Why is it that the magnetic field of a current carrying coil having n turns, is ‘n’ times as large as that produced by a single turn (loop)?
Ans: Magnetic field produced by a current carrying wire at a given pint depends directly on the current passing through it. So if there is a circular coil having ‘n’ turns, the field produced is n times as large as that produced by a single turn. This is because the current in each circular turn has the same direction and the field due to each turn just adds up.
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)