31/ 1/2 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) The change in magnetic field lines in a coil is the cause of induced electric current in it. Name the underlying phenomenon.
Ans: Electromagnetic Induction
(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) The compound obtained on reaction of iron with steam is/are:
(a) Fe2O3
(b) Fe3O4
(c) Feo
(d) Fe2O3 and Fe3O4
Or
An element ‘X’ reacts with O2 to give a compound with a high melting point. This compound is also soluble in water. The element ‘x’ is likely to be:
(a) iron
(b) calcium
(c) carbon
(d) silicon
(6)The laws of reflection hold true for:
(a) plane mirrors only
(b) concave mirrors only
(c) convex mirrors only
(d) all reflecting surfaces
Ans: All reflecting surface
Or
When an object is kept within the focus of a concave mirror, an enlarged image is formed behind the mirror. The image is:
(a) real
(b) inverted
(c) virtual and inverted
(d) virtual and erect
Ans: Virtual and erect
(7) At the time of short circuit, the electric current in the circuit:
(a) vary continuously
(b) does not change
(c) virtual and inverted
(d) virtual and erect
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: 1A
(8) The chemical formula for plaster of Paris is:
(a) CaSo4. 2H2O
(b) CaSo4. H2O
(c) CaSo4.1/2 H2O
(d) 2 CaSO4. H2O
Ans: CaSO4.1/ 2 H2O
(9) 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
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)
(10) Baking soda is a mixture of:
(a) Sodium carbonate and acetic acid
(b) Sodium carbonate and tartaric acid
(c) Sodium hydrogen carbonate and tartaric acid
(d) Sodium hydrogen carbonate and acetic acid
Ans: (c)/ Sodium hydrogen carbonate and tartaric acid
(11) In an ecosystem, 10% of energy available for transfer from one trophic level to the next is in the form of:
(a) heat energy
(b) chemical energy
(c) mechanical energy
(d)Support life
Ans: Chemical energy.
(12) Soil fertility is determined by its ability to:
(a) Decay organic matter
(b) Hold organic matter
(c) Hold water
(d) Support life
Ans: Support life
(13) Assertion (A): In a homologous series of alcohols, the formula of the second member is C2H5OH and the third member is C3H7OH.
Reason (R): The difference between the molecular masses of the two consecutive members of a homologous series is 144.
Ans: (c) / A is true but R is false
(14) Assertion (A): In the process of nuclear fission, the amount of nuclear energy generated by the fission of an atom of uranium is so tremendous that it produces 10 million times the energy produced by the combustion of an atom of carbon from cola.
Reason (R): The nucleus of a heavy atom such as uranium, when bombarded with low energy neutrons, splits apart into lighter nuclei. The mass difference between the original nucleus and the product nuclei gets converted to tremendous energy.
Ans: (a) / Both (A) and (R) are true and ( R) is the correct explanation of the assertion (A).
SECTION – B
(15) What is ‘rusting’ Describe with a labeled diagram an activity to investigate the conditions under which iron rusts.
Ans:
- Oxidation of iron when exposed to air and moisture and acquiring a coating of brown flaky substance.
Activity –
• Take three test tubes marked A,B and C with clean iron nails in each.
• Pour some water in test tube ‘A’ and cork it.
• Pour some boiled distilled water and a drop of oil in test tube B and cork it.
• Put some anhydrous calcium chloride in test tube ‘C’ and cork it. It will absorb moisture from air leave the test tubes for a few days.
• Rusting will take place only in test tube A, which has air and moisture present.
(16) 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.
(17) 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.
(18) Draw a labeled 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:
(19) (a) List in tabular form two differences between binary fission and multiple fission.
Ans:
BINARY FISSION | MULTIPLE FISSION |
The parent body divides into two identical daughter cells. | Parent body show several nuclear division producing many daughter cells. |
Occurs only in favourable conditions | Occurs in favourable/unfavourble conditions. |
(b) What happens when a mature Spirogyra filament attains considerable length.
Ans: A mature spirogyra breaks into smaller pieces and each fragment develops into a new organism
(20) 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
(21) 3 mL of ethanol is taken in a test tube and warmed gently in a water bath. A 5% solution of alkaline potassium permanganate is added first drop by drop to this solution, then in excess.
(i) How is 5% solution of KMnO4 prepared?
Ans: (i) By dissolving 5g of KMnO4 in 100mL of water/ By dissolving 5g of KMnO4 in water to make a final volume of 100 mL.
(ii) State the role of alkaline potassium permanganate is this reaction. What happens on adding it in excess?
Ans: As an oxidizing agent Purple colour persists
(iii) Write chemical equation of this reaction.
Ans:
(22) A squirrel is in a scary situation. Its body has to prepare for either fighting or running away. State the immediate changes that take place in its body so that the squirrel is able to either fight or run?
Ans:
- The adrenaline hormone is secreted into the blood.
- The heart beats faster resulting in supply of more oxygen to the muscles.
- Blood is diverted to skeletal muscles.
- The breathing rate increases.
- The blood supply to digestive systems and skin is reduced.
Or
Why is chemical communication better than electrical impulses as a means of communication between cells in a multi – cellular organism?
Ans:
- Electrical impulses have limited access to only those cells that are connected by nervous tissue/ neurons, whereas chemical signals can reach each and every cell of the body .
- Cells need time to reset in order to create repeated/ new electrical impulses whereas no such time is required for chemical communication.
(23) (a) State the relation correlating the electric current flowing in a conductor and the voltage applied across it. Also draw a graph to show this relationship.
Ans: V α I or / = constant
or V = 1R
(any of these)
(b) Find the resistance of a conductor if the electric current flowing through it is 0.35 A when the potential difference across it is 1.4 V.
Ans: given I = 0.35 A,
V = 1.4 V
R = V/1
= 1.4/0.35
= 4.Ὠ
(24) (a) Write the mathematical expression for Joule’s law of heating.
Ans: (i) H = I2Rt
(b) Compute the hate generated while transferring 96000 coulomb of charge in two hours through a potential difference of 40 V.
(ii) H = V.I.t = V.Q
Given : V = 40 volts , Q = 96000 C
H = 40 V × 96000 C
= 3.84 × 106 J
SECTION – C
(25) (a) What is thermit process? Where is the process used? Write balanced chemical equation for the reaction involved.
Ans:
- The highly exothermic displacement reaction between iron oxide and aluminum powder.
- It is used to join railway tracks or cracked machine parts.
- Fe2O3(s)+ 2 Al(s) → Fe(l) + Al2O3(s) + Heat
(b) Where does the metal aluminium, used in the process, occurs in the reactivity series of metals?
Ans: It is placed above iron / towards top in the reactivity series.
(c) Name the substance that are getting oxidised and reduced in the process.
Ans: Oxidized → Al.
Reduced → Fe2O3
(26) (a) What is an electromagnet? List any two uses.
Ans: A current carrying solenoid is called an electromageet /when soft iron is placed inside a solenoid carrying current, the soft iron piece behaves like a magnet so long as electric current passes through it. The magnet so formed is electromagnet.
Uses: In electric motors, electric bells,
(b) Draw a labelled diagram to show how an electromagnet is made.
(c) State the purpose of soft iron core used in making an electromagnet.
Ans: Soft iron core is used to increase the strength/power of the electro magnet.
(d) List two ways of increasing the strength of an electromagnet if the material of the electromagnet is fixed.
Ans: (i) By increasing the current
(ii) By increasing the number of turns in the coil.
(27) 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 is 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.
(28) (a) What is genetics?
Ans: a).Study of heredity and variations in organisms
(b) What are genes? Where are the genes located?
Ans: b). • Gene – A segment of DNA which is a carrier of genetic information from one generation to another.
(c) State and define three factors responsible for the rise of a new species.
Ans: (i) Natural selection – selection of the fittest organisms which are then transferred over generations leading to the evolution of a new species.
(ii) Genetic drift – It is the random change in the frequency of genes in a small population over successive generations.
(iii) Reproductive isolation–when some members of a particular species are not able to mate with other members of the same species due to geographical/environmental barriers leading to origin of a new species.
(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) Why is there a difference in the rate of breathing between aquatic organisms and terrestrial organisms? Explain.
Ans: Rate of breathing is faster in aquatic organisms because the amount of dissolved oxygen in water is lower as compared to the amount of oxygen in air.
(b) Draw a diagram of human respiratory system and label – pharynx, trachea, lungs, diaphragm, and alveolar sac on it.
Ans:
Or
(c) Name the organs that form the excretory system in human beings.
Ans: A pair of kidneys, a pair of ureters, a urinary bladder and a urethra.
(d) Describe in brief how urine is produced in human body.
Ans: A kidney has a large number of filtration units called nephrons. Each nephron has a bunch of capillaries called glomerulus. Blood containing nitrogenous waste gets filtered in the glomerulus. Filtrate gets collected in Bowman’s capsule. Some substances such as glucose amino acids, salts and water are selectively reabsorbed as urine flows through nephron tube.The urine formed in each kidney is eventually stored in the urinary bladder
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)
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- 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)