Class 10 Science: CBSE (Official) Marking Scheme with Solution (2020-21) | Science Class 10 PDF Download

 Page 1


 
1 
MARKING SCHEME 
SAMPLE QUESTION PAPER 2020-21 
CLASS X (SCIENCE) 
 
No. Value Points Marks 
1 • Initial light green colour changes to reddish brown colour 
• Colourless gas is evolved 
• Gas with choking smell is evolved  
(Any two) 
OR 
Sodium Chloride and Hydrogen gas 
1 
 
2. Sodium Carbonate decahydrate, Na
2
CO
3
.10H
2
O 1 
3. a. Change in chemical properties 
It does not occur due to the presence of the same functional group. 
1 
4. The light is least scattered at noon. 1 
5. Both are concave. 
Alternative answer that should be given credit: Plano-concave lens 
1 
6 Between the principal focus and the centre of curvature. 
OR 
Optical centre. 
1 
7 There are momentary galvanometer deflections that die out shortly; the 
deflections are in opposite directions. 
1 
8 The field consists of concentric circles centred on the wire 
 
 
 
1 
9 Voltage-drop is same across both 
OR 
W=QV 
1 
10 Veins have thin walls because the blood there is no longer under 
pressure and they have valves to ensure blood flow in one direction. 
1 
Page 2


 
1 
MARKING SCHEME 
SAMPLE QUESTION PAPER 2020-21 
CLASS X (SCIENCE) 
 
No. Value Points Marks 
1 • Initial light green colour changes to reddish brown colour 
• Colourless gas is evolved 
• Gas with choking smell is evolved  
(Any two) 
OR 
Sodium Chloride and Hydrogen gas 
1 
 
2. Sodium Carbonate decahydrate, Na
2
CO
3
.10H
2
O 1 
3. a. Change in chemical properties 
It does not occur due to the presence of the same functional group. 
1 
4. The light is least scattered at noon. 1 
5. Both are concave. 
Alternative answer that should be given credit: Plano-concave lens 
1 
6 Between the principal focus and the centre of curvature. 
OR 
Optical centre. 
1 
7 There are momentary galvanometer deflections that die out shortly; the 
deflections are in opposite directions. 
1 
8 The field consists of concentric circles centred on the wire 
 
 
 
1 
9 Voltage-drop is same across both 
OR 
W=QV 
1 
10 Veins have thin walls because the blood there is no longer under 
pressure and they have valves to ensure blood flow in one direction. 
1 
 
2 
11 The inner lining of the small intestine has numerous finger-like 
projections called villi which increase the surface area for absorption. 
 
OR 
Goat because herbivores eating grass need a longer small intestine to 
allow the cellulose to be digested. 
1 
12 Ozone layer protects us from harmful effects of UV radiation. 
OR 
The loss of energy at each step is so great that very little usable energy 
remains after four trophic levels. 
1 
13 The pancreas secretes digestive juice which contains enzymes like 
trypsin for digesting proteins and lipase for breakdown of emulsified 
fats.   
1 
14 c) Assertion is True & Reason is False 1 
15 b) Both Assertion & Reasoning are correct, Reason is not correct 
explanation of Assertion 
OR 
b) Both Assertion & Reasoning are correct, Reason is not correct 
explanation of Assertion 
1 
16 a) Both Assertion & Reasoning are correct & Reason is the correct 
explanation of Assertion 
1 
17 (i) b) Tissue respiration 1 
(ii) b) Anaerobic respiration 1 
(iii) 
 
b) Aerobic  Anaerobic  Amount of energy is high 
and consistent in aerobic 
and low in anaerobic 
1 
(iv) c) ii), iii), iv) only  1 
(v) a) Location Aerobic-Cytoplasm and Anaerobic-Mitochondria  
 
1 
18 (i) c) Cs>Rb>K>Na>Li 1 
(ii) b) As Hydrogen can easily lose one electron like alkali metals to form 
positive ion 
1 
(iii) a) F  1 
(iv) c) Electronegativity decreases down the group due to increase in atomic 
radius/ tendency to gain electron decreases. 
1 
(v) d) F and Li are in the same period and across the period atomic 1 
Page 3


 
1 
MARKING SCHEME 
SAMPLE QUESTION PAPER 2020-21 
CLASS X (SCIENCE) 
 
No. Value Points Marks 
1 • Initial light green colour changes to reddish brown colour 
• Colourless gas is evolved 
• Gas with choking smell is evolved  
(Any two) 
OR 
Sodium Chloride and Hydrogen gas 
1 
 
2. Sodium Carbonate decahydrate, Na
2
CO
3
.10H
2
O 1 
3. a. Change in chemical properties 
It does not occur due to the presence of the same functional group. 
1 
4. The light is least scattered at noon. 1 
5. Both are concave. 
Alternative answer that should be given credit: Plano-concave lens 
1 
6 Between the principal focus and the centre of curvature. 
OR 
Optical centre. 
1 
7 There are momentary galvanometer deflections that die out shortly; the 
deflections are in opposite directions. 
1 
8 The field consists of concentric circles centred on the wire 
 
 
 
1 
9 Voltage-drop is same across both 
OR 
W=QV 
1 
10 Veins have thin walls because the blood there is no longer under 
pressure and they have valves to ensure blood flow in one direction. 
1 
 
2 
11 The inner lining of the small intestine has numerous finger-like 
projections called villi which increase the surface area for absorption. 
 
OR 
Goat because herbivores eating grass need a longer small intestine to 
allow the cellulose to be digested. 
1 
12 Ozone layer protects us from harmful effects of UV radiation. 
OR 
The loss of energy at each step is so great that very little usable energy 
remains after four trophic levels. 
1 
13 The pancreas secretes digestive juice which contains enzymes like 
trypsin for digesting proteins and lipase for breakdown of emulsified 
fats.   
1 
14 c) Assertion is True & Reason is False 1 
15 b) Both Assertion & Reasoning are correct, Reason is not correct 
explanation of Assertion 
OR 
b) Both Assertion & Reasoning are correct, Reason is not correct 
explanation of Assertion 
1 
16 a) Both Assertion & Reasoning are correct & Reason is the correct 
explanation of Assertion 
1 
17 (i) b) Tissue respiration 1 
(ii) b) Anaerobic respiration 1 
(iii) 
 
b) Aerobic  Anaerobic  Amount of energy is high 
and consistent in aerobic 
and low in anaerobic 
1 
(iv) c) ii), iii), iv) only  1 
(v) a) Location Aerobic-Cytoplasm and Anaerobic-Mitochondria  
 
1 
18 (i) c) Cs>Rb>K>Na>Li 1 
(ii) b) As Hydrogen can easily lose one electron like alkali metals to form 
positive ion 
1 
(iii) a) F  1 
(iv) c) Electronegativity decreases down the group due to increase in atomic 
radius/ tendency to gain electron decreases. 
1 
(v) d) F and Li are in the same period and across the period atomic 1 
 
3 
size/radius decreases from left to right. 
19 (i) b) Convex 1 
(ii) P=1/f 
P
1
=1/f
1
 and P
2
=1/f
2
 
P
1
/P
2
=4/1, hence (1/f
1
)/(1/f
2
) = 4/1 
Hence f
1
/f
2
=1/4  
b) ¼ 
1 
(iii) a) Ratio of height of image to height of object  1 
(iv) m=v/u 
3=24/u 
Hence u = 8cm 
c) 8 cm 
1 
(v) c) Not-so-thick lenses would not make the telescope very heavy and 
they will also allow considerable amount of light to pass through them. 
1 
20 (i) c. Electrical to Mechanical 1 
(ii) b. The bar will be magnetised as long as there is current in the circuit. 1 
(iii) a. A bar magnet 1 
(iv) d. Only II 1 
(v) a. For a current of 0.8A the magnetic field is 13 mT 1 
Section B 
21 Bile juice makes the acidic food coming from the stomach alkaline for 
the action of pancreatic enzymes. Bile salts break the large globules of 
fat in the intestine to smaller globules increasing the efficiency of 
enzyme action. This is similar to the emulsifying action of soaps on dirt. 
OR 
The separation keeps oxygenated and deoxygenated blood from mixing 
allowing a highly efficient supply of oxygen to the body. This is useful 
in animals that have high energy needs (birds and mammals) which 
constantly use energy to maintain their body temperature. 
 
2 
 
 
 
 
 
 
 
 
 
22 
 
Absorption of light energy by chlorophyll. 
• Conversion of light energy to chemical energy and splitting of 
water molecules into hydrogen and oxygen. 
• Reduction of carbon dioxide to carbohydrates. 
 
2 
 
 
 
 
 
Page 4


 
1 
MARKING SCHEME 
SAMPLE QUESTION PAPER 2020-21 
CLASS X (SCIENCE) 
 
No. Value Points Marks 
1 • Initial light green colour changes to reddish brown colour 
• Colourless gas is evolved 
• Gas with choking smell is evolved  
(Any two) 
OR 
Sodium Chloride and Hydrogen gas 
1 
 
2. Sodium Carbonate decahydrate, Na
2
CO
3
.10H
2
O 1 
3. a. Change in chemical properties 
It does not occur due to the presence of the same functional group. 
1 
4. The light is least scattered at noon. 1 
5. Both are concave. 
Alternative answer that should be given credit: Plano-concave lens 
1 
6 Between the principal focus and the centre of curvature. 
OR 
Optical centre. 
1 
7 There are momentary galvanometer deflections that die out shortly; the 
deflections are in opposite directions. 
1 
8 The field consists of concentric circles centred on the wire 
 
 
 
1 
9 Voltage-drop is same across both 
OR 
W=QV 
1 
10 Veins have thin walls because the blood there is no longer under 
pressure and they have valves to ensure blood flow in one direction. 
1 
 
2 
11 The inner lining of the small intestine has numerous finger-like 
projections called villi which increase the surface area for absorption. 
 
OR 
Goat because herbivores eating grass need a longer small intestine to 
allow the cellulose to be digested. 
1 
12 Ozone layer protects us from harmful effects of UV radiation. 
OR 
The loss of energy at each step is so great that very little usable energy 
remains after four trophic levels. 
1 
13 The pancreas secretes digestive juice which contains enzymes like 
trypsin for digesting proteins and lipase for breakdown of emulsified 
fats.   
1 
14 c) Assertion is True & Reason is False 1 
15 b) Both Assertion & Reasoning are correct, Reason is not correct 
explanation of Assertion 
OR 
b) Both Assertion & Reasoning are correct, Reason is not correct 
explanation of Assertion 
1 
16 a) Both Assertion & Reasoning are correct & Reason is the correct 
explanation of Assertion 
1 
17 (i) b) Tissue respiration 1 
(ii) b) Anaerobic respiration 1 
(iii) 
 
b) Aerobic  Anaerobic  Amount of energy is high 
and consistent in aerobic 
and low in anaerobic 
1 
(iv) c) ii), iii), iv) only  1 
(v) a) Location Aerobic-Cytoplasm and Anaerobic-Mitochondria  
 
1 
18 (i) c) Cs>Rb>K>Na>Li 1 
(ii) b) As Hydrogen can easily lose one electron like alkali metals to form 
positive ion 
1 
(iii) a) F  1 
(iv) c) Electronegativity decreases down the group due to increase in atomic 
radius/ tendency to gain electron decreases. 
1 
(v) d) F and Li are in the same period and across the period atomic 1 
 
3 
size/radius decreases from left to right. 
19 (i) b) Convex 1 
(ii) P=1/f 
P
1
=1/f
1
 and P
2
=1/f
2
 
P
1
/P
2
=4/1, hence (1/f
1
)/(1/f
2
) = 4/1 
Hence f
1
/f
2
=1/4  
b) ¼ 
1 
(iii) a) Ratio of height of image to height of object  1 
(iv) m=v/u 
3=24/u 
Hence u = 8cm 
c) 8 cm 
1 
(v) c) Not-so-thick lenses would not make the telescope very heavy and 
they will also allow considerable amount of light to pass through them. 
1 
20 (i) c. Electrical to Mechanical 1 
(ii) b. The bar will be magnetised as long as there is current in the circuit. 1 
(iii) a. A bar magnet 1 
(iv) d. Only II 1 
(v) a. For a current of 0.8A the magnetic field is 13 mT 1 
Section B 
21 Bile juice makes the acidic food coming from the stomach alkaline for 
the action of pancreatic enzymes. Bile salts break the large globules of 
fat in the intestine to smaller globules increasing the efficiency of 
enzyme action. This is similar to the emulsifying action of soaps on dirt. 
OR 
The separation keeps oxygenated and deoxygenated blood from mixing 
allowing a highly efficient supply of oxygen to the body. This is useful 
in animals that have high energy needs (birds and mammals) which 
constantly use energy to maintain their body temperature. 
 
2 
 
 
 
 
 
 
 
 
 
22 
 
Absorption of light energy by chlorophyll. 
• Conversion of light energy to chemical energy and splitting of 
water molecules into hydrogen and oxygen. 
• Reduction of carbon dioxide to carbohydrates. 
 
2 
 
 
 
 
 
 
4 
These steps need not take place one after the other immediately. 
For example, desert plants take up carbon dioxide at night and 
prepare an intermediate which is acted upon by the energy 
absorbed by the chlorophyll during the day 
 
23 - Burn compound in air/ oxygen; Gas evolved turns lime water 
milky 
 
- By sharing its four valence electrons with other elements.    
OR 
• Due to self linking ability of carbon/catenation 
• Since carbon has a valency of four it can form bonds with four 
other atoms of carbon or atoms of some other mono-valent 
element. 
• Due to small size of carbon it forms very strong and (or) stable 
bonds with other elements 
(Any two) 
1 
 
 
1 
 
 
 
 
 
1 + 1  
 
24 i. S>R>P>Q 
ii. Cu and QSO
4
 
1 
1  
25 The phenomenon is called dispersion. 
Speed of Violet Light inside the prism is slowest and that of Red is 
highest. Hence, deviation of Violet Light is maximum and that of Red is 
minimum. 
1 
 
1 
 
26 The overall current needed = 9A. The voltage is 12V 
Hence by Ohm’s Law V=IR, 
The resistance for the entire circuit = 12/9 = 4/3 O. = R 
R
1
 and R
2
 are in parallel. 
Hence, R=(R
1 
R
2
)/(R
1
 + R
2
) = 4R
2
/(4+R
2
) = 4/3 
R
2
 = 2O 
 
2 
Section- C 
27 The ratio obtained is 9:3:3:1 in which parental as well as new 
combinations are observed. This indicates that progeny plants have not 
inherited a single whole gene set from each parent. 
Every germ cell takes one chromosome from the pair of maternal and 
paternal chromosomes. When two germ cells combine, segregation of 
one pair of characters is independent of other pair of characters. 
OR 
In human beings, the genes inherited from our parents decide whether 
we will be boys or girls. Women have a perfect pair of sex 
chromosomes (XX). But, men have a mismatched pair (XY). 
 
3 
 
 
Page 5


 
1 
MARKING SCHEME 
SAMPLE QUESTION PAPER 2020-21 
CLASS X (SCIENCE) 
 
No. Value Points Marks 
1 • Initial light green colour changes to reddish brown colour 
• Colourless gas is evolved 
• Gas with choking smell is evolved  
(Any two) 
OR 
Sodium Chloride and Hydrogen gas 
1 
 
2. Sodium Carbonate decahydrate, Na
2
CO
3
.10H
2
O 1 
3. a. Change in chemical properties 
It does not occur due to the presence of the same functional group. 
1 
4. The light is least scattered at noon. 1 
5. Both are concave. 
Alternative answer that should be given credit: Plano-concave lens 
1 
6 Between the principal focus and the centre of curvature. 
OR 
Optical centre. 
1 
7 There are momentary galvanometer deflections that die out shortly; the 
deflections are in opposite directions. 
1 
8 The field consists of concentric circles centred on the wire 
 
 
 
1 
9 Voltage-drop is same across both 
OR 
W=QV 
1 
10 Veins have thin walls because the blood there is no longer under 
pressure and they have valves to ensure blood flow in one direction. 
1 
 
2 
11 The inner lining of the small intestine has numerous finger-like 
projections called villi which increase the surface area for absorption. 
 
OR 
Goat because herbivores eating grass need a longer small intestine to 
allow the cellulose to be digested. 
1 
12 Ozone layer protects us from harmful effects of UV radiation. 
OR 
The loss of energy at each step is so great that very little usable energy 
remains after four trophic levels. 
1 
13 The pancreas secretes digestive juice which contains enzymes like 
trypsin for digesting proteins and lipase for breakdown of emulsified 
fats.   
1 
14 c) Assertion is True & Reason is False 1 
15 b) Both Assertion & Reasoning are correct, Reason is not correct 
explanation of Assertion 
OR 
b) Both Assertion & Reasoning are correct, Reason is not correct 
explanation of Assertion 
1 
16 a) Both Assertion & Reasoning are correct & Reason is the correct 
explanation of Assertion 
1 
17 (i) b) Tissue respiration 1 
(ii) b) Anaerobic respiration 1 
(iii) 
 
b) Aerobic  Anaerobic  Amount of energy is high 
and consistent in aerobic 
and low in anaerobic 
1 
(iv) c) ii), iii), iv) only  1 
(v) a) Location Aerobic-Cytoplasm and Anaerobic-Mitochondria  
 
1 
18 (i) c) Cs>Rb>K>Na>Li 1 
(ii) b) As Hydrogen can easily lose one electron like alkali metals to form 
positive ion 
1 
(iii) a) F  1 
(iv) c) Electronegativity decreases down the group due to increase in atomic 
radius/ tendency to gain electron decreases. 
1 
(v) d) F and Li are in the same period and across the period atomic 1 
 
3 
size/radius decreases from left to right. 
19 (i) b) Convex 1 
(ii) P=1/f 
P
1
=1/f
1
 and P
2
=1/f
2
 
P
1
/P
2
=4/1, hence (1/f
1
)/(1/f
2
) = 4/1 
Hence f
1
/f
2
=1/4  
b) ¼ 
1 
(iii) a) Ratio of height of image to height of object  1 
(iv) m=v/u 
3=24/u 
Hence u = 8cm 
c) 8 cm 
1 
(v) c) Not-so-thick lenses would not make the telescope very heavy and 
they will also allow considerable amount of light to pass through them. 
1 
20 (i) c. Electrical to Mechanical 1 
(ii) b. The bar will be magnetised as long as there is current in the circuit. 1 
(iii) a. A bar magnet 1 
(iv) d. Only II 1 
(v) a. For a current of 0.8A the magnetic field is 13 mT 1 
Section B 
21 Bile juice makes the acidic food coming from the stomach alkaline for 
the action of pancreatic enzymes. Bile salts break the large globules of 
fat in the intestine to smaller globules increasing the efficiency of 
enzyme action. This is similar to the emulsifying action of soaps on dirt. 
OR 
The separation keeps oxygenated and deoxygenated blood from mixing 
allowing a highly efficient supply of oxygen to the body. This is useful 
in animals that have high energy needs (birds and mammals) which 
constantly use energy to maintain their body temperature. 
 
2 
 
 
 
 
 
 
 
 
 
22 
 
Absorption of light energy by chlorophyll. 
• Conversion of light energy to chemical energy and splitting of 
water molecules into hydrogen and oxygen. 
• Reduction of carbon dioxide to carbohydrates. 
 
2 
 
 
 
 
 
 
4 
These steps need not take place one after the other immediately. 
For example, desert plants take up carbon dioxide at night and 
prepare an intermediate which is acted upon by the energy 
absorbed by the chlorophyll during the day 
 
23 - Burn compound in air/ oxygen; Gas evolved turns lime water 
milky 
 
- By sharing its four valence electrons with other elements.    
OR 
• Due to self linking ability of carbon/catenation 
• Since carbon has a valency of four it can form bonds with four 
other atoms of carbon or atoms of some other mono-valent 
element. 
• Due to small size of carbon it forms very strong and (or) stable 
bonds with other elements 
(Any two) 
1 
 
 
1 
 
 
 
 
 
1 + 1  
 
24 i. S>R>P>Q 
ii. Cu and QSO
4
 
1 
1  
25 The phenomenon is called dispersion. 
Speed of Violet Light inside the prism is slowest and that of Red is 
highest. Hence, deviation of Violet Light is maximum and that of Red is 
minimum. 
1 
 
1 
 
26 The overall current needed = 9A. The voltage is 12V 
Hence by Ohm’s Law V=IR, 
The resistance for the entire circuit = 12/9 = 4/3 O. = R 
R
1
 and R
2
 are in parallel. 
Hence, R=(R
1 
R
2
)/(R
1
 + R
2
) = 4R
2
/(4+R
2
) = 4/3 
R
2
 = 2O 
 
2 
Section- C 
27 The ratio obtained is 9:3:3:1 in which parental as well as new 
combinations are observed. This indicates that progeny plants have not 
inherited a single whole gene set from each parent. 
Every germ cell takes one chromosome from the pair of maternal and 
paternal chromosomes. When two germ cells combine, segregation of 
one pair of characters is independent of other pair of characters. 
OR 
In human beings, the genes inherited from our parents decide whether 
we will be boys or girls. Women have a perfect pair of sex 
chromosomes (XX). But, men have a mismatched pair (XY). 
 
3 
 
 
 
5 
All children will inherit an X chromosome from their mother regardless 
of whether they are boys or girls. Thus, the sex of the children will be 
determined by what they inherit from their father. A child who inherits 
an X chromosome from her father will be a girl, and one who inherits a 
Y chromosome from him will be a boy. 
28 Use of Plastic cups raised the concern towards hygiene thus they were 
replaced by disposable plastic cups. 
Plastic cups are non-biodegradable and harm the environment friendly. 
They were thus replaced by Kulhads. 
Making Kulhad made of clay on a large scale resulted in the loss of top 
fertile soil. 
Now, disposable paper cups are used because - the paper can be 
recycled, it is biodegradable and is eco-friendly material which does not 
cause environmental pollution.   
 
 
3 
29 - Blood passes through filtration units in the kidney called nephron  
- Passes through glomerulus in the Bowman's capsule - Ultra 
filtration  
- Filtrate initially has glucose, amino acids, water, salts and 
nitrogenous waste  
- Reabsorption – Water (as per the need of the body), Glucose and 
amino acids are all reabsorbed –  
- Secretion of excess water, salts and urea (nitrogenous waste) 
which makes up the urine  
3 
30 
a. Heating of lead nitrate; and electrolysis of acidified water 
 
b.   
              Sunlight 
    2AgCl
(s)                                       
2Ag
(s)
 + Cl
2  (g)   
 
    (No deduction for not mentioning state of reactants and products.) 
2 
 
 
 
 
 
 
1 
31 (i) D, As it is on the left side of the table in group 2 
(ii) C, as it is in the group 18/ Noble gas 
(iii) E, as we move from left to right across a period, atomic radius 
decreases 
1 
 
1 
 
1