31/2/2 2020 Class 10 Science Question Paper Solution
Section – A
(1) How many metals are present in second period of periodic table ?
Ans: Two / Lithium and Beryllium
(2) Covalent compounds have low melting and boiling point. Why ?
Ans: Due to weak intermolecular forces.
(3) Answer question numbers 4(a) to 4(d) on the basis of your understanding of the following information and related studied concepts.
Thyroid gland is a bilobed structure situated in our neck region. It secretes a hormone called thyroxine. Iodine is necessary for the thyroid gland to make thyroxine. Thyroxine regulates carbohydrate, protein and fat metabolism in the body. It promotes growth of body tissues also. When there is an excess of thyroxine in the body, a person suffers from hyperthyroidism and if this gland is underactive it results in hypothyroidism. Hyperthyroidism is diagnosed by blood tests that measure the levels of thyroxine and Thyroid Stimulating Hormone (TSH). Hypothyroidism is caused due to the deficiency of iodine in our diet resulting in a disease called goitre. Iodised salt can be included in our diet to control it.
(a) Where is thyroid gland situated in our body ?
Ans: In the neck region
(b) State the function of thyroxine in human body.
Ans: Thyroxine regulates carbohydrate, proteins and fat metabolism in the body./ It promotes growth of body tissue.
(c) What is hyperthyroidism ?
Ans: Excess of secretion of throxine in the body /overactivity of the thyroid gland
(d) How can we control hypothyroidism ?
Ans: Can be controlled by including iodised salt in our diet.
(4) Answer question numbers 3(a) to 3(d) on the basis of your understanding of the following paragraph and the related studied concepts.
Geothermal energy is the energy produced by the heat of molten rocks formed in the deeper hot regions of the earth’s crust. This energy is harnessed to generate electricity. When water is made to flow deep underground in the rocks it returns as steam (or hot water, which is later converted to steam) to drive a turbine on an electric power generator.
In India, exploration and study of geothermal fields started in 1970. The Geological Survey in India has identified 350 geothermal energy locations in the country. The most promising of these is in Puga valley of Ladakh. The estimated potential for geothermal energy in India is about 10000 MW. There are seven geothermal provinces in India namely the Himalayas, Sohna, West coast, Cambay, Son-Narmada-Tapi; Godavari and Mahanadi. Most power stations in India produce Alternating Current (A.C).
(a) What are geothermal energy hot-spots ?
Ans: Are deeper hot regions of earth’s crust where molten rocks are formed.
(b) Name two countries, other than India, where power plants based on geothermal energy are operational.
Ans: New Zealand / United States of America / China/Indonesia, Philippines / Turkey/ New Mexico.
(c) Name the phenomenon that explains the working of an electric generator.
Ans: Electromagnetic Induction.
(d) State an important advantage of using AC over DC.
Ans: In case of A.C. transmission of power/electricity takes place without much loss of energy.
(5) On the basis of electronic configuration of 9 5 X, the group number and period of the element ‘X’ is:
(a) Group 15 period 2
(b) Group 13 period 2
(c) Group 9 period 5
(d) Group 13 period 5
Ans: Group 13 period 2
OR
An element ‘X’ with atomic number 11 forms a compound with element ‘Y’ with atomic number 8. The formula of the compound formed is
(a) XY
(b) X2Y
(c) XY2
(d) X2Y3
Ans: X2Y
(6) A visually challenged student, has to perform a lab test to detect the presence of acid in a given solution. The acid-base indicator preferred by him will be:
(a) Blue litmus
(b) Clove oil
(c) Red cabbage extract
(d) Hibiscus extract
Ans: Clove oil
(7) Identify ‘x’, ‘y’ and ‘z’ in the following reaction :
2 KClO3 ¾®¾¾(x) ( y) 2 KCl (x) + O2 (z)
(a) x = gas ; y = reaction condition, z = gas
(b) x = solid ; y = liquid; z = gas
(c) x = number of moles of KClO3 ; y = reaction condition; z = no. of molecules of oxygen.
(d) x = physical state of KClO3 and KCl; y = reaction condition; z = physical state of O2.
Ans: x= Physical state of KClO3 and KCl
y = Reaction condition
z= Physical state of O2
(8) Bandharas and Tals are age old water harvesting concepts / structures found in
(a) Bihar
(b) Maharashtra
(c) Tamil Nadu
(d) Rajasthan
Ans: Maharashtra
(9) Which of the following are water intensive crops?
(a) Wheat and rice
(b) Wheat and sugarcane
(c) Sugarcane and rice
(d) Wheat and gram
Ans: Sugarcane and rice
OR
The most poisonous product formed by incomplete combustion of fossil fuels is
(a) Carbon dioxide
(b) Nitrogen dioxide
(c) Carbon monoxide
(d) Sulphur dioxide
Ans: Carbon monoxide
(10) The maximum resistance which can be made using four resistors each of 2 W is
(a) 2 W
(b) 4 W
(c) 8 W
(d) 16 W
Ans: 8Ω
(11) Consider the following reasons for the reddish appearance of the sun at the sunrise or the sunset:
(a) Light from the sun near the horizon passes through thinner layers of air.
(b) Light from the sun covers larger distance of the earth’s atmosphere before reaching our eyes.
(c) Near the horizon, most of the blue light and shorter wavelengths are scattered away by the particles.
(d) Light from the sun near the horizon passes through thicker layers of air.
Ans: (b)
The correct reasons are
(a) A and C only
(b) B, C and D
(c) A and B only
(d) C and D only
Ans: B,C and D
OR
Person suffering from cataract has
(a) elongated eyeball
(b) excessive curvature of eye lens
(c) weakened ciliary muscles
(d) opaque eye lens
Ans: Opaque eye lens
(12) A student plots V-I graphs for three samples of nichrome wire with resistances R1 , R2 and R3 . Choose from the following the statement that holds true for this graph.
(a) R1 = R2 = R3
(b) R1 > R2 > R3
(c) R3 > R2 > R1
(d) R2 > R1 > R3
Ans: R2 > R1 > R3
For question numbers 13 and 14, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
(a) Both (A) and (R) are true and (R) is correct explanation of the assertion.
(b) Both (A) and (R) are true but (R) is not the correct explanation of the assertion.
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
(13) Assertion (A) : The metals and alloys are good conductors of electricity.
Reason (R) : Bronze is an alloy of copper and tin and it is not a good conductor of electricity.
Ans: (d) / (A) is false, but (R) is true.
(14) Assertion (A) : Ethanoic acid is also known as glacial acetic acid.
Reason (R) : The melting point of pure ethanoic acid is 290 K and hence it often freezes during winters in cold climates.
Ans: (a) / Both (A) and (R) are true and (R) is the correct explanation of the assertion.
Section – B
(15) (i) Only one half of water molecule is shown in the formula of Plaster of Paris.
Ans: 2 formula units of CaSO4 /Calcium sulphate share 1 molecule of water of crystallization.
(ii) Sodium hydrogen carbonate is used as an antacid.
Ans: due to its alkaline nature.
(iii) On strong heating, blue coloured copper sulphate crystals turn white.
Ans: CuSO4 + 5H2O → CuSO4 .5H2O
(Blue) (White)
/ Due to loss of water of crystallization.
OR
(i) Draw a labelled diagram to show the preparation of hydrogen chloride gas in laboratory.
Ans:
(ii) Test the gas evolved first with dry and then with wet litmus paper. In which of the two cases, does the litmus paper show change in colour?
Ans: Wet litmus paper
(iii) State the reason of exhibiting acidic character by dry HCl gas / HCl solution.
Ans: HCl solution , it is due to the formation of H + ion on in the water / H3O + (Hydronium ions)
(16) A compound ‘A’ is used in the manufacture of cement. When dissolved in water, it evolves a large amount of heat and forms compound ‘B’.
(i) Identify A and B.
Ans: A = CaO / Quick lime/ Calcium oxide B = Ca(OH)2 / Slaked lime / Calcium hydroxide
(ii) Write chemical equation for the reaction of A with water.
Ans: CaO + H2O → Ca(OH)2 + heat or energy
(iii) List two types of reaction in which this reaction may be classified.
Ans: Combination reaction
Exothermic reaction
(17) The position of three elements A, B and C in the Modern periodic table is as follows:
(a) Write formula of compound formed betwee :
(i) B and ;
Ans: BA
(ii) B and C
Ans: B2C
(b) Is any of the three elements a metal ? Give reason to justify your answer.
Ans: None
- Because none of them show any characteristics of metal.
(18) Complete the following flow chart as per the given instructions:
Ans:
Secretions | Functions |
(a) mucus | (d)Protects the inner lining of stomach from the acid / softening of food |
(b) HCl(Hydrochloric acid) | (e)Provides the acidic medium for action of enzyme / Kill the germs. |
(c) Pepsin | (f) Digest proteins |
(19) (a) Construct a terrestrial food chain comprising four trophic levels.
Ans: Grass → Grass hopper → Frog → Snake
(b) What will happen if we kill all the organisms in one trophic level?
Ans: Transfer of food energy to the next higher level will not take place , then the organisms of the upper trophic levels will be affected , increase in the population of the organisms belonging to the previous trophic level / imbalance in the food chain.
(c) Calculate the amount of energy available to the organisms at the fourth trophic level if the energy available to the organisms at the second trophic level is 2000 J.
Ans:
OR
(a) Complete the following table:
Oxygen | Ozone | |
Formula | (i) O2 | (ii) O3 |
Benefits to biotic component | (iii) Breathing /Respiration | (iv) Absorbs harmful ultra violet (UV) radiations. |
(b) How is ozone formed at the higher levels of atmosphere?
Ans:
(20) (a) What are fossils?
Ans:
- Fossils are the preserved remains or impressions of the animals/ plants of remote past.
(b) Describe two methods of determining the age of fossils.
Ans:
- Two methods:
(i) Relative Methods: Fossils closer to the surface are more recent than those found in the deeper layers.
(ii) Dating fossils: Detecing the ratio of different isotopes of same element in the fossils.
(21) (a) Why did Mendel carry out an experiment to study inheritance of two traits in garden-pea?
Ans: To show independent inheritance of traits/ Independent assortment.
(b) What were his findings with respect to inheritance of traits in F1 and F2 generation?
Ans: In F1 progeny : All dominant traits.
In F2 progeny : original parental and new combinations are visible.
(c) State the ratio obtained in the F2 generation in the above mentioned experiment.
Ans: 9:3:3:1
(22) Two coils of insulated copper wire are wound over a non-conducting cylinder as shown. Coil 1 has comparative large number of turns. State your observations, when
(i) Key K is closed.
Ans: Galvanometer (G) shows deflection (for very short time)
(ii) Key K is opened
Ans: Galvanometer (G) shows deflection for a very short time in opposite direction to the previous observation.
Give reason for each of your observations.
Ans: Common Reason: Due to variation in current flowing through coil 1, magnetic field associated with coil 2 changes. Due to which an induced current will generate consequently galvanometer shows momentry defelection.
(23) (a) List two causes of hypermetropia.
Ans: (i) Size of eyeball decreases
(ii) Focal length of eye lens is too long / Power of eye lens decreases.
(b) Draw ray diagrams showing
(i) a hypermetropic eye and
(ii) its correction using suitable optical device.
OR
(a) State the relation between colour of scattered light and size of the scattering particle.
Ans: Small size particles scatter shorter wavelength (violet) or large sized particles scatter larger wavelength (Red).
(b) The apparent position of an object, when seen through the hot air, fluctuates or wavers. State the basic cause of this observation.
Ans: Due to variation in physical condition of hot air.
(c) Complete the path of white light when it passes through two identical prisms placed as shown:
Ans:
(Splitting of white light is essential )
(24) Draw ray diagrams for the following cases when a ray of light:
(i) passing through centre of curvature of a concave mirror is incident on it.
Ans:
(ii) parallel to principal axis is incident on convex mirror.
Ans:
(iii) is passing through focus of a concave mirror incident on it.
Ans:
Section – C
(25) (a) What is a homologous series ? Explain with an example.
- Homologous series: is a group of compounds which have the same functional group , same general formula and where to successive member differ by – CH2 in the molecular formula
Example : CH3-OH , CH3 -CH2-OH
Functional group : -OH , General Formula : CnH2n OH
(b) Define the following terms giving one example of each.
(i) Esterification
(ii) Addition reaction
Ans: Esterification: The reaction of carboxylic acid with an alcohol in the presence of H2SO4 yields an ester.
CH3COOH+C2H5OH Photo CH3COOC2H5 + H20
Addition Reaction: A reaction in which two or more atoms are added across a double or triple bond in presence of catalyst is called addition reactions.
CH2=CH2+H2 Photo CH3-CH3
(26) (a) Complete and balance the following chemical equations:
(i) Al2 O3 + HCl →
Ans: Al2CI3 + 3 H2O→ + 3 H2O
(ii) K2O + H2O →
Ans: K2O + H2O → 2 KOH
(iii) Fe + H2O →
Ans: 3 Fe + 4 H2O→ 3 Fe + 4 H2O
(b) An element ‘X’ displaces iron from the aqueous solution of iron sulphate. List your observations if the element ‘X’ is treated with the aqueous solutions of copper sulphate, zinc sulphate and silver nitrate. Based on the observations arrange X, Zn, Cu and Ag in increasing order of their reactivities.
OR
(a) Name the following:
(i) Metal that can be cut by knife
Ans: Sodium (Na) / Potassium (K)
(ii) Lustrous non-metal
Ans: Iodine (I)
(iii) Metal that exists in liquid state at room temperature
Ans: Mercury (Hg)
(iv) Most malleable and ductile metal
Ans: Gold (Au)
(v) Metal that is best conductor of electricity
Ans: Silver / Copper
(vi) Non-metal that can exist in different forms
Ans: Carbon / Sulphur / Phosphorous
(b) How are alloys better than metals ? Give composition of solder and amalgam.
Ans: They are generally stronger / have high tensile strength / high electrical resistivity / resistant to corrosion.
- Solder : Lead + Tin / Pb + Sn
Amalgam – an alloy in which mercury is one of the constituent / Any metal + mercury
(27) (a) List three different categories of contraception methods.
Ans: · Chemical Method
- Barrier Method
- Surgical Method
(b) Why has Government of India prohibited prenatal sex determination by law ? State its benefits in the long run.
Ans: Increase in female foeticide / Declining child sex ratio
Benefit : Maintaining male-female sex ratio for a healthy society
(c) Unsafe sexual act can lead to various infections. Name two bacterial and two viral infections caused due to unsafe sex.
Ans: Bacterial → Gonorrhoea
Syphilis
Viral → Warts
AIDS
OR
(a) In the female reproductive system of human beings, state the funtions of
(i) ovary (ii) oviduct
Ans: (i) Ovary → Production of female germ cell/egg Production of hormone – estrogen
(ii) Oviduct → Site of fertilization
(b) Mention the changes which the uterus undergoes, when
(i) it has to receive a zygote.
Ans: Thickening of the uterus lining
(ii) no fertilization takes place.
Ans: Wall of uterus breaks/Menstruation occurs.
(c) State the function of placenta.
Ans: Providing the nutrition / O2/to the developing embryo /foetus or removal of waste from the fetus.
(28) (a) “Blood circulation in fishes is different from the blood circulation in human beings.” Justify the statement.
Ans: In fish :
- 2 chambered heart
- Single Circulation
In Human beings:
- 4 chambered heart
- Double circulation.
(b) Describe “blood circulation” in human beings.
Ans:
- The deoxygenated blood from all body parts is collected by the veins to pour into venacava.
- Vena cava pours blood into the right atrium(RA).
- Right atrium transfers this blood into the right ventricle (RV).
- Right ventricle pumps blood to lungs through pulmonary artery.
- The oxygenated blood from the lungs is brought to the left atrium (LA) through pulmonary vein.
- Now the blood is pumped to left ventricle, from where the blood is distributed to all parts of the body through Aorta.
(29) (a) A concave mirror of focal length 10 cm can produce a magnified real as well as virtual image of an object placed in front of it. Draw ray diagrams to justify this statement.
Ans: (i) Real and magnified
Object distance must be between 10 to 20 cm
Virtual and magnified
Object distance must be less than 10 cm
(b) An object is placed perpendicular to the principal axis of a convex mirror of focal length 10 cm. The distance of the object from the pole of the mirror is 10 cm. Find the position of the image formed.
Ans: f = 10 cm ; u = – 10 cm
1/V + 1/U = 1/f
1/v = 1/f – 1/u
1/v = 1/10 -1/10
1/v = 1/10 +1/10
1/v = 1/5 ∴ v = 5cm
OR
(a) Define the following terms :
(i) Power of a lens
Ans: Ability of a lens to converge or diverge light rays/reciprocal of focal length of lens.
(ii) Principal focus of a concave mirror
Ans: It is a point on principal axis at which light ray parallel to principal axis converges after reflection.
(b) Write the relationship among the object distance (u), image distance
(V) and the focal length (f) of a
(i) Spherical lens
Ans: (i) for spherical lens: 1/v – 1/u = 1/f
(ii) Spherical mirror
Ans: (ii) for spherical mirror: 1/v + 1/u = 1/f
(c) An object is placed at a distance of 10 cm from optical centre of a convex lens of focal length 15 cm. Draw a labelled ray diagram to show the formation of image in this case.
Distance of object (BO) = 10 cm
Focal length (OF1 ) = 15 cm
(30) A 6 W resistance wire is doubled on itself. Calculate the new resistance of the wire.
Ans: In this case : Length L becomes l/2 then Area of cross section A become 2A
R = ρ L/A = 6 Ω
R = ρ L/2/2A
R’ = 1/4 ρ L/A
R’ = 1/4 X 6
R’ = 3/2 Ω
(b) Three 2 W resistors A, B and C are connected in such a way that the total resistance of the combination is 3 W. Show the arrangement of the three resistors and justify your answer.
Ans: No of resistors = 3 Each resistor has resistance = 2Ω
In this arrangement where total resistance is 3Ω
- Resistor A of 2Ω is connected in series with a parallel combination of the resistors B (2Ω) and C (2Ω).
- Arrangement :
- Total resistance R = 2Ω + 2Ω×2Ω/ 2Ω+2Ω
R= 2Ω + 4Ω/ 4Ω
= 2Ω + 1Ω
R = 3Ω
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)