31/5/3 2020 Class 10 Science Question Paper Solution
SCIENCE
SECTION A
1) Assertion (A) : Carbon has a strong tendency to either lose or gain electrons to attain noble gas configuration.
Reason (R) : Carbon has four electrons in its outermost shell and has the tendency to share electrons with carbon or other elements.
Ans: (iv) / (A) is false, but (R) is true
2) Assertion (A) : At high temperatures, metal wires have a greater chance of short circuiting.
Reason (R) : Both resistance and resistivity of a material vary with temperature.
Ans: (ii) / Both (A) and (R) are true, but (R) is not the correct explanation of the assertion(A)
3) Covalent compounds are generally poor conductors of electricity. Why ?
Ans: No charged particles/ions
4) State the common characteristic of the following elements : Boron, Silicon, Germanium and Arsenic
Ans: All are metalloids/Shows the properties of metals and non-metals
OR
State the Periodic Law on which the Modern Periodic Table is based.
Ans: Properties of elements are a periodic function of their atomic number
5) Answer question numbers 5(a) – 5(d) on the basis of your understanding of the following paragraph and the related studied concepts :
Solar power in India is a fast developing industry. The country’s solar installed capacity reached 30·071 GW as of 31 July, 2019. India has the lowest capital cost per MW to install solar power plants. Solar electricity generation recorded nearly 3·4% of total utility electricity generation in January 2019. The following table shows Annual Solar Power Generation of the last six years.
Year |
Solar Power Generation (TWh) |
2013 – 14 |
3·35 |
2014 – 15 |
4·60 |
2015 – 16 |
7·45 |
2016 – 17 |
12·09 |
2017 – 18 |
25·87 |
2018 – 19 |
39·27 |
Our country is lucky to receive solar energy for the greater part of the year. It is estimated that during a year India receives the energy equivalent to more than 5000 trillion kWh from the Sun.
5(a) What are solar cells ?
Ans: Cells which convert solar energy to electrical energy/electricity
5(b) How much voltage can be developed and how much electricity can be produced by one typical solar cell when exposed to the Sun ?
Ans: Voltage – 0.5 to 1V
Electricity –0.7W
5(c) The future of power generation by solar energy is bright in India. Give reason.
Ans: India receives great amount of solar energy throughout the year.
5(d) List two advantages of solar cells.
Ans: Advantages :- No moving parts/require little maintenance /work quite satisfactorily without any focusing device/can be set up in remote and inaccessible areas.
6) Question numbers 6(a) – 6(d) are based on the table and related information in the passage given below.
Thyroid Stimulating Hormone (TSH) stimulates thyroid gland to produce thyroxine. Study the table given below.
Table : TSH levels during pregnancy
Stage of pregnancy | Normal (mU/L) | Low (mU/L) | High (mU/L) |
First trimester | 0·2 – 2·5 | < 0·2 | 2·5 – 10 |
Second trimester | 0·3 – 3·0 | < 0·3 | 3·01 – 4·5 |
Third trimester | 0·8 – 5·2 | < 0·8 | > 5·3 |
It is important to monitor TSH levels during pregnancy. High TSH levels and hypothyroidism can especially affect chances of miscarriage. Therefore, proper medication in consultation with a doctor is required to regulate/control the proper functioning of the thyroid gland.
6(a) Give the full form of TSH.
Ans: Thyroid stimulating hormone.
6(b) State the main function of TSH.
Ans: It stimulates / regulates thyroid gland to produce thryroid hormone or thyroxine.
6(c) Why do TSH levels in pregnant women need to be monitored ?
Ans: Because high and low TSH level may increase the chances of miscarriage.
6(d) A pregnant woman has TSH level of 8·95 mU/L. What care is needed for her ?
Ans: Proper medication is required.
7) The values of mA and mA are
(A) 10–6 A and 10–9 A respectively
(B) 10–3 A and 10–6 A respectively
(C) 10–3 A and 10–9 A respectively
(D) 10–6 A and 10–3 A respectively
Ans: (B) 10–3 A and 10–6 A respectively
8) A cylindrical conductor of length ‘l’ and uniform area of cross-section ‘A’ has resistance ‘R’. Another conductor of length 2·5 l and resistance 0·5 R of the same material has area of cross-section
(A) 5 A
(B) 2·5 A
(C) 0·5 A
(D) 1/5( A)
Ans: (A) / 5A
9) The image distance from the eye lens in the normal eye when we increase the distance of an object from the eye
(A) increases.
(B) decreases.
(C) remains unchanged.
(D) depends on the size of the eyeball.
Ans: (C) remains unchanged.
10) The Reni village of Garhwal is famous for
(A) Monocultures of pine, teak and eucalyptus.
(B) Chipko Movement.
(C) Extensive biodiversity.
(D) Participation of local people in efficient management of forests.
Ans: (B)/ Chipko Movement
11) Consider the following criticisms that are generally addressed when a new project is launched :
I.) Displacement of peasants and local tribals without compensation.
II.) Swallowing up large amount of public money without any benefits.
III.) Deforestation and loss of biodiversity.
The criticisms about large dams in particular are
(A) I and II
(B) II and III
(C) I and III
(D) I, II and III
Ans: (D) /I , II and III
OR
Switching off unnecessary lights and fans and repairing leaking taps correctly defines which term of 5R’s ?
(A) Recycle
(B) Reuse
(C) Repurpose
(D) Reduce
Ans: (D) / Reduce
12) Strong heating of ferrous sulphate leads to the formation of a brown solid and two gases. This reaction can be categorised as
(A) displacement and redox.
(B) decomposition and redox.
(C) displacement and endothermic.
(D) decomposition and exothermic.
Ans: (B) / Decomposition & Redox
13) If 10 mL of H2SO4 is mixed with 10 mL of Mg(OH)2 of the same concentration, the resultant solution will give the following colour with universal indicator :
(A) Red
(B) Yellow
(C) Green
(D) Blue
Ans: (C)/ Green
14) An element X with atomic number 12 forms a compound with element Y with atomic number 17. The formula of the compound formed is
(A) XY
(B) XY2
(C) X2Y
(D) X2Y3
Ans: (B) / XY2
OR
An element X is forming acidic oxide. Its most probable position in the modern periodic table is
(A) Group 1 and Period 3
(B) Group 16 and Period 3
(C) Group 17 and Period 3
(D) Group 2 and Period 3
Ans: (B ) / (C)
SECTION B
15) Identify the type of each of the following reactions stating reason for your answers :
(a) Fe2O3 + 2Al -> Al2O3 + 2Fe + heat
Ans: Displacement /Redox/ Exothermic reaction/Thermit reaction.
Displacement- Iron is displaced by aluminium
Redox : Aluminium is oxidised and Iron is reduced
Exothermic- Heat is produced
Thermit reaction: Molten iron is produced.
(b) Pb(NO3 )2 + 2KI -> PbI2 + 2KNO3
Ans: Double displacement reaction
Ions are exchanged between the reactants
Ans: Decomposition reaction /Calcination
ZnCO3 decomposes to ZnO+CO2
16) From the elements Li, K, Mg, C, Al, S identify the
(a) elements belonging to the same group.
Ans: Li ,K
(b) element which has the tendency to lose two electrons.
Ans: Mg
(c) element which prefers sharing of electrons to complete its octet.
Ans: C
(d) most metallic element.
Ans: K
(e) element that forms acidic oxide.
Ans: S
(f) element that belongs to group 13.
Ans: Al
17) In the electrolysis of water
(a) Name the gases liberated at anode and cathode.
Ans: Anode- Oxygen Cathode- Hydrogen
(b) Why is it that the volume of gas collected on one electrode is two times that on the other electrode ?
Ans: Because one molecule of water contains two atoms of hydrogen and one atom of oxygen/ 2H2O->2H2+O2
(c) What would happen if dil. H2SO4 is not added to water ?
Ans: Electrolysis of water will not take place
OR
A chemical compound ‘X’ is used in the soap and glass industry. It is prepared from brine.
(a) Write the chemical name, common name and chemical formula of ‘X’.
Ans: Chemical Name – Sodium Carbonate decahydrate Common Name – Washing Soda Chemical Formula – Na2CO3 . 10H2O
(b) Write the equation involved in its preparation.
Ans: NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3
Na2CO3 + 10H2O -> Na2CO3 . 10H2O
(c) What happens when it is treated with water containing Ca or Mg salts ?
Ans: It helps in removing permanent hardness./ It forms insoluable Ca or Mg salts in the form of scum
18) (a) Create a food chain of the following organisms : Insect, Hawk, Grass, Snake, Frog
Ans: Grass -> Insect-> Frog -> Snake -> Hawk
(b) Name the organism at the third trophic level of the created food chain.
Ans: Frog
(c) Which organism of this food chain will have the highest concentration of non-biodegradable chemicals ?
Ans: Hawk
(d) Name the phenomenon associated with it.
Ans: Biomagnification
(e) If 10,000 joules of energy is available to frogs, how much energy will be available to snakes in this food chain ?
Ans: 1000J
OR
(a) What is an ecosystem ?
Ans: All interacting organisms in an area together with non living constituents of the environment form an ecosystem.
(b) List any two natural ecosystems.
Ans: Forest/Pond/Terrestrial /any other
(c) We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly. Why ?
Ans: Decomposers are present in ponds or lakes; whereas these are absent in an aquarium.
19) What provides nutrition to human sperms ? State the genetic constitution of a sperm.
Ans: (a)
- Secretions from seminal vesicle.
- 22+X and 22+Y
(b) Mention the chromosome pair present in zygote which determines the sex of (i) a female child, and (ii) a male child.
Ans: (i) Female-XX
(ii) Male – XY
20) (a) In the process of respiration, state the function of alveoli.
Ans: Exchange of gases.
(b) Rate of breathing in aquatic organisms is much faster than that in terrestrial organisms. Give reasons.
Ans: Because amount of oxygen dissolved in water is fairly low as compared to the air
(c) Complete the following pathway showing the breakdown of glucose :
Ans: (i) Pyruvate
(ii) Carbon dioxide
21) (a) Why is the F1 progeny always of tall plants when a tall pea plant is crossed with a short pea plant ?
Ans: Because Tallness is the dominant trait
(b) How is F2 progeny obtained by self-pollination of F1 progeny different from F1 progeny ? Give reason for this observation.
Ans: The recessive character is expressed in the F2 generation when two copies of the recessive trait are present together/(tt).
(c) State a conclusion that can be drawn on the basis of this observation.
Ans: In the F2 progeny , the dominant character is also expressed along with the recessive character in ratio of 3:1 respectively.
22) Draw ray diagram in each of the following cases to show what happens after reflection to the incident ray when
(a) it is parallel to the principal axis and falling on a convex mirror.
Ans:
(b) it is falling on a concave mirror while passing through its principal focus.
Ans:
(c) it is coming oblique to the principal axis and falling on the pole of a convex mirror.
Ans:
23) A student uses spectacles of focal length – 2·5 m.
(a) Name the defect of vision he is suffering from.
Ans: Myopia/Short sightedness
(b) Which lens is used for the correction of this defect ?
Ans: Concave/Diverging lens.
(c) List two main causes of developing this defect.
Ans:
- Excessive curvature of eye lens
- elongation of eye ball
(d) Compute the power of this lens.
Ans: P(D) = 1/ f(m)
P(D) = 1/ −2.5(m) = 10 /−25 = 2 /−5 = −0.4D
OR
Give reasons :
(a) Red colour is selected for danger signals.
Ans: The Red colour is least scattered by fog or smoke, hence visible from a long distance.
(b) The sky appears dark in space.
Ans: Because in the absence of atomosphere there is no scattering of light
(c) The time difference between actual sunset and apparent sunset is about 2 minutes.
Ans: Because of atmospheric refraction, the sun appears above the horizon even after actual sunset.
24) (a) Draw the pattern of magnetic field lines due to a magnetic field through and around a current carrying circular loop.
Ans:
(b) Name and state the rule to find out the direction of magnetic field inside and around the loop.
Ans:
- Right hand thumb rule.
- When a current carrying straight conductor is held in the right hand in such a way that the thumb points towards the direction of the current, then the fingers will wrap around the conductor in the direction of the field lines of the magnetic field
SECTION C
25) (a) Define isomerism. Draw all possible isomers of butane.
Ans: When two or more organic compounds have same molecular formula but different structural formula , then the compounds are called isomers and this phenomenon is called isomerism
(b) ‘‘A compound ‘X’ on combustion gives a yellow flame with lots of smoke.’’ What inference would you draw from this statement ?
Ans: Because ‘X’ is an unsaturated carbon compound
(c) State the role of alkaline KMnO4 in the reaction involving conversion of an alcohol to corresponding carboxylic acid.
Ans: Oxidising agent.
26) (a) What is an amalgam ?
Ans: An alloy in which one of the constituent is mercury.
(b) Why is solder used for making electrical fuse ?
Ans: Because of its lower melting point.
(c) What is galvanisation ? State its significance.
Ans:
- When iron/steel articles are coated with a thin layer of zinc.
- It protects the articles from rusting.
(d) In the electrolytic refining of copper, name the anode and cathode used and the electrolyte taken in the cell.
Ans: Anode – Impure copper
Cathode – Pure copper
Electrolyte – Acidified copper sulphate solution
OR
(a) Explain the formation of ionic compound, Al2O3 with electron-dot structure : (Given : Atomic no. of Al and O are 13 and 8 respectively)
Ans: Electronic configuration
Al O
2,8,3 2,6
(b) What happens when (Report only observations)
(i) a reactive metal reacts with a dilute mineral acid ?
Ans: Hydrogen gas is evolved
(ii) an amphoteric oxide reacts with sodium hydroxide solution ?
Ans: Salt and water are formed/Oxide gets dissolved.
(iii) a metal of low reactivity is dropped in the salt solution of a metal of high reactivity ?
Ans: No reaction
(iv) a metal carbonate is treated with acid ?
Ans: Brisk effervescence.
27) (a) List two reasons of using contraceptive methods by married couples.
Ans:
- Preventing unwanted pregnancies.
- Prevention of STDs/Sexually transmitted diseases
- Keeping gap between children
(b) Write in proper sequence the processes going on in the different organs of the reproductive system of a human female starting from the time of egg production to childbirth.
Ans:
OR
(a) Identify the modes of asexual reproduction in each of the following organisms :
(i) Hydra
Ans: Budding
(ii) Planaria
Ans: Regeneration
(iii) Amoeba
Ans: Binary fission
(iv) Spirogyra
Ans: Fragmentation
(v) Rhizopus
Ans: Spore formation
(b) List three advantages of vegetative propagation.
Ans:
- Vegetative propagation help those plants to grow that have lost the power of producing seeds.
- The plants produced through Vegetative propagation are genetically similar to their parents.
- These plants bear fruits earlier than plants produced from seeds.
(c) Why can fertilisation not take place in flowers if pollination does not occur ?
Ans: If the pollination does not occur the pollen grains are not transferred to stigma of a flower, no fertilization will take place
28) Give reasons :
(a) Ventricles have thicker muscular walls than atria.
Ans: Because ventricles have to pump blood to various distant organs of the body
(b) Transport system in plants is slow.
Ans: Because their energy requirement is low
(c) Circulation of blood in aquatic vertebrates differs from that in terrestrial vertebrates.
Ans: In aquatic vertebrates the blood goes only once through the heart during one cycle while in terrerstrial vertebrates it goes through the heart two times during each cycle.
(d) During the daytime, water and minerals travel faster through xylem as compared to the night.
Ans: Because transpirational pull is greater during day time.
(e) Veins have valves whereas arteries do not.
Ans: To prevent the backflow of the blood /blood flows only in one direction
29)a) Complete the following ray diagram:
Ans:
(b) Find the nature, position and size of the image formed.
Ans: Virtual, erect and magnified
(c) Use lens formula to determine the magnification in this case.
Ans: u = -18 cm; f = 20 cm
1/ f = 1 /v − 1 /u
1/ 20 = 1 /v − 1 /−18
1 /20 = 1 /v + 1 /18
1 /v = 1/ 20 − 1 /18
= 18 − 20 /360 = −1 /180
∴ v = −180cm
Magnification = v/u = −180/ −18 = +10
OR
(a) Complete the following ray diagram :
Ans:
(b) Find the nature, position and size of the image formed.
Ans: Virtual , erect and magnified
(c) Use mirror formula to determine the magnification in this case.
Ans: f = -30 cm u = -15 cm
1/ f = 1/ v + 1/ u
1 /−30 = 1 /v + 1 /−15
1 /v = − (1 /30) + 1/ 15 = 1/ 30
∴ v = 30cm
Magnification = −v /u = −30 /−15 = 2
30) (a) Two lamps rated 100 W, 220 V and 10 W, 220 V are connected in parallel to 220 V supply. Calculate the total current through the circuit.
Ans: I1 = P1 /V
I1 = 100 W /220 V = 10 /22 A
I2 = P2 /V = 10 /220 = 1 /22 A
I = I1 + I2
= (10 /22 + 1/ 22) A = 11/ 22 A = 0.5 A
(b) Two resistors X and Y of resistances 2 Ω and 3 Ω respectively are first joined in parallel and then in series. In each case the voltage supplied is 5 V.
(i) Draw circuit diagrams to show the combination of resistors in each case.
Ans:
(ii) Calculate the voltage across the 3 Ω resistor in the series combination of resistors.
Ans: Net R=R1+R2=2+3=5 Ω
I = V / = 5/ 5 = 1A
∴ Voltage across 3 Ω resistor
∴ V = 1 × 3 = 3V
CBSE Class 10 Previous Question Paper 2020 Solution
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