31/5/2 2020 Class 10 Science Question Paper Solution
SCIENCE
SECTION A
1) 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
2) Covalent compounds are generally poor conductors of electricity. Why ?
Ans: No charged particles/ions
3) Question numbers 3(a) – 3(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.
3(a) Give the full form of TSH.
Ans: Thyroid stimulating hormone.
3(b) State the main function of TSH.
Ans: It stimulates / regulates thyroid gland to produce thryroid hormone or thyroxine.
3(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.
3(d) A pregnant woman has TSH level of 8·95 mU/L. What care is needed for her ?
Ans: Proper medication is required.
4) Answer question numbers 4(a) – 4(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.
4(a) What are solar cells ?
Ans: Cells which convert solar energy to electrical energy/electricity
4(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
4(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.
4(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.
5) 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
6) 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.
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) 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
9) 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
10) 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)
11) 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
12) 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
13) 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)
14) 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
SECTION B
15) 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
16) A shining metal ‘M’, on burning gives a dazzling white flame and changes to a white powder ‘N’.
(a) Identify ‘M’ and ‘N’.
Ans: (a) ‘M’ is magnesium /Mg ‘N’ is Magnesium oxide / MgO
(b) Represent the above reaction in the form of a balanced chemical equation.
Ans: (b) 2Mg + O2 -> 2MgO
(c) Does ‘M’ undergo oxidation or reduction in this reaction ? Justify.
Ans: ‘M’ undergoes oxidation because oxygen is added to it/ Loss of 2 electrons
17) (a) List any two distinguishing features between Mendeleev’s Periodic Table and the Modern Periodic Table.
Ans:
Mendeleev’s Periodic Table |
Modern Periodic Table |
Based on atomic mass of elements |
Based an atomic number of elements |
It has 8 groups |
It has 18 groups |
Except 8th group all groups are divided in A & B sub groups |
No sub groups |
Two or more elements are placed in the same group |
Each element is placed in separate group |
Some elements with higher atomic mass are placed before elements with lower atomic mass |
No such anomalies |
No place for isotopes |
Isotopes find place in it |
(b) With the help of an example, explain Dobereiner’s Triads.
Ans: Example – Li , Na , K The atomic mass of the middle element is an average of the atomic masses of other two elements.
(c) State Modern Periodic Law.
Ans: Properties of elements are a periodic function of their atomic number
18) (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
19) What is meant by trophic level in a food chain ? Construct a terrestrial food chain with four trophic levels. The energy flow in a food chain is always unidirectional. Why ?
Ans:
- Trophic level – Each step or level of a food chain forms a trophic level
- Grass → Insect → Frog →Snake/Hawk /
- Because it moves progressively through the various trophic levels and is no longer available to the previous level from producers to consumers.
OR
Complete the following flow chart based on ecosystem and its components.
Ans: (i) Aquatic
(ii) Abiotic
(iii) Air/Water/Soil/Temperature /Non-living
(iv) Living organism/plants and animals
(v) Definition – All the interacting organisms in an area together with the non living constituents of the environment form an ecosystem /interaction between biotic and abiotic components.
20) (a) 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
21) Define the following : (a) Speciation
Ans: Speciation- The origin of a new species from the pre existing one
(b) Natural Selection
Ans: Natural selection – Nature selects the best traits in a species , leading to survival of the fittest and evoloution of species.
(c) Genetic Drift
Ans: Genetic drift – Accidental changes in the frequency of genes.
22) A child is standing in front of a magic mirror. She finds the image of her head bigger, the middle portion of her body of the same size and that of the legs smaller. Explain the construction of the magic mirror using different types of mirrors. Also state the reasons in support of your answer.
Ans: The top part of the mirror is concave because it forms enlarged ,erect and virtual image when the object is closer to the mirror. The middle part is a plain mirror because it forms image of the same size
The lower part is a convex mirror because it forms erect and diminished image.
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) A coil of insulated wire is connected to a galvanometer. What would be observed if a strong bar magnet with its south pole towards one face of the coil is
(i) moved quickly toward it ?
Ans: Momentary deflection in the needle of the galvanometer to the left / right.
(ii) moved quickly away from it ?
Ans: Momentary deflection in the needle of the galvanometer but in the opposite direction.
(iii) held stationary near it ?
Ans: No deflection
(b) Name the phenomena involved.
Ans: Electromagnetic induction.
(c) State the conclusion based on the observations in (i), (ii) and (iii).
Ans: Motion of a magnet with respect to coil induces an electric current in the coil which lasts so long as the motion is taking place / change in magnetic field around a coil produces an induced current in it.
SECTION C
25) Consider the molecular formula of the carbon compounds (a) and (b) given below :
(a) C3H8O (b) C3H6O2 (i) Identify the functional groups in (a) and
Ans: –OH group /Alcoholic group ; CH3-CH2-CH2-OH
(b) and write their structures.
Ans:
(ii) Are (a) and (b) isomers ? Give reason.
Ans:
- No
- Because they have different molecular formula.
(iii) What happens when alkaline KMnO4 is added, drop by drop, into a test tube containing warm propanol ? Write the chemical equation for the reaction and state the role of alkaline KMnO4 in this reaction.
Ans: Propanoic acid is formed
- Oxidising agent
26) Two ores X and Y were taken. On heating these ores it was observed that
(a) ore X gives CO2 gas, and
(b) ore Y gives SO2 gas. Write steps to convert these ores into metals, giving chemical equations of the reactions that take place.
Ans:
The metal oxide is reduced by using suitable reducing agent such as carbon.
ZnO( s) + C s → Zn(s) + CO(g)
OR
(a) With the help of a diagram explain the method of refining of copper by electrolysis.
Ans:
- Impure copper is made the anode and thin strip of pure copper is made the cathode.
- A solution of acidified copper sulphate is taken as electrolyte
( Note : Labelled diagram is to be awarded full marks)
On passing the current the pure metal from the anode dissolves into the electrolyte and equivalent amount of pure metal is deposited on the cathode.
(b) How are broken railway tracks joined ? Give the name of the process and the chemical equation of the reaction involved.
Ans:
- By filling the gaps with molten iron formed in the reaction of Fe2O3 with aluminum powder.
- Thermit process/reaction
- Fe2O3(s)+2Al(s)-> 2Fe(l)+Al2O3(s)+Heat
27) Based on the given diagram answer the questions given below :
(a) Label the parts A, B, C and D.
Ans:
- A-> Ureter
- B-> seminal vesicle
- C-> Urethra
- D-> Vas deferens
(b) Name the hormone secreted by testis and mention its role.
Ans: Testosterone : Role
- Regulates the formation of sperms
- Changes in appearance of boys at the time of puberty.
(c) State the functions of B and C in the process of reproduction.
Ans: Function of ‘B’
- Providing nutrition and transportation to sperms.
Function of ‘C’
- Serves as a common passage to both sperms and urine.
OR
(a) Name the mode of reproduction of the following organisms and state the important feature of each mode :
(i) Planaria
(ii) Hydra
(iii) Rhizopus
Ans : Regeneration- the lost body part can be regenerated.
- Budding – a complete small individual develops on the parent body during favourable conditions.
- Spore Formation – Spores are covered with thick wall that helps to overcome unfavourable conditions.
(b) We can develop new plants from the leaves of Bryophyllum. Comment.
Ans: Buds produced in the notches along the leaf margins develop into new plants.
(c) List two advantages of vegetative propagation over other modes of reproduction.
Ans: Advantages :
- Propagation of flowerless plants.
- Genetically similar to the parent plant.
- Plants raised by vegetative propagation bear flowers and fruits earlier than those produced from seeds.
28) Design an activity to show that chlorophyll is essential for photosynthesis.
Ans:
- Take a potted plant with variegated leaves.
- Keep the plant in a dark room for three days so that all the starch gets used up.
- Keep the plant in sunlight for about six hours.
- Pluck a leaf from this plant. Mark the green areas in it and trace them on a sheet of paper.
- Dip the leaf in boiling water for a few minutes.
- After this, immerse it in a beaker containing alcohol.
- Carefully place the above beaker in a water-bath and heat till the alcohol begins to boil.
- Now dip the leaf in a dilute solution of iodine for a few minutes.
- Take out the leaf and rinse off the iodine solution.
Observation: The green parts of the leaf have turned blue –black.
Inference : This indicates the presence of starch formed during photosynthesis.
29) (a) Draw a labelled ray diagram to show the path of a ray of light incident obliquely on one face of a glass slab.
Ans:
(b) Calculate the refractive index of the material of a glass slab. Given that the speed of light through the glass slab is 2 × 108 m/s and in air is 3 × 108 m/s.
Ans: nga = Speed of light in air/ Speed of light in glass = 3×108 /2×108 = 3/ 2 = 1.5
(c) Calculate the focal length of a lens, if its power is – 2·5 D.
Ans: f (m) = 1 /P (D)
f = 1 /P = 1/ −2.5D = −10 /25D = −0.4m
(Note –Deduct ½ marks if unit is not mentioned)
OR
(a) A person suffering from myopia (near-sightedness) was advised to wear corrective lens of power – 2·5 D. A spherical lens of same focal length was taken in the laboratory. At what distance should a student place an object from this lens so that it forms an image at a distance of 10 cm from the lens ?
Ans: f(m) = 1/ P(D)
f = 1/ −2.5D = −10 /25D = −0.4m = −40cm
f=-40 cm
v =-10 cm u = ?
1/ v – 1/ u = 1/ f
1 /−10 cm − 1 /u = 1 /−40 cm
− 1/ u = 1 /−40 + 1 /10
= −1 + 4/ 40 = 3 /40
∴ u = − 40 /3 =−13.3 cm
(b) Draw a ray diagram to show the position and nature of the image formed in the above case.
Ans: Since the power is –ve , the lens used is concave / diverging
OA = v = -10cm ; OB = u =-13.3 cm ; OF = f = -40cm
30) (a) State Ohm’s Law.
Ans: The potential difference ,V , across the ends of a given metallic wire in an electric circuit is directly proportional to the current flowing through it, provided its temperature remains the same.
(b) How is an ammeter connected in an electric circuit ?
Ans: In Series
(c) The power of a lamp is 100 W. Find the energy consumed by it in 1 minute.
Ans: Energy Consumed = P×t
= 100× 60s
6000J
(d) A wire of resistance 5 W is bent in the form of a closed circle. Find the resistance between two points at the ends of any diameter of the circle.
Ans:
1 / = 1/ 1 + 1 /2
1 = 2.5Ω ; R2=2.5Ω
∴ 1/ = 1 /2.5 + 1 /2.5 = 2 /2.5
= 2.5 /2 = 1.25Ω
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)