Download Central Board of Secondary Education (CBSE) Class 10th (10th Board Exam) Science Marking Scheme 2021 Model Paper
SAMPLE QUESTION PAPER 2020-21
CLASS X (SCIENCE)
No.
Value Points
Marks
1
? Initial light green colour changes to reddish brown colour
1
? Colourless gas is evolved
? Gas with choking smell is evolved
(Any two)
OR
Sodium Chloride and Hydrogen gas
2.
Sodium Carbonate decahydrate, Na2CO3.10H2O
1
3.
a. Change in chemical properties
1
It does not occur due to the presence of the same functional group.
4.
The light is least scattered at noon.
1
5.
Both are concave.
1
Alternative answer that should be given credit: Plano-concave lens
6
Between the principal focus and the centre of curvature.
1
OR
Optical centre.
7
There are momentary galvanometer deflections that die out shortly; the
1
deflections are in opposite directions.
8
The field consists of concentric circles centred on the wire
1
9
Voltage-drop is same across both
1
OR
W=QV
10
Veins have thin walls because the blood there is no longer under
1
pressure and they have valves to ensure blood flow in one direction.
1
11
The inner lining of the small intestine has numerous finger-like
1
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.
12
Ozone layer protects us from harmful effects of UV radiation.
1
OR
The loss of energy at each step is so great that very little usable energy
remains after four trophic levels.
13
The pancreas secretes digestive juice which contains enzymes like
1
trypsin for digesting proteins and lipase for breakdown of emulsified
fats.
14
c) Assertion is True & Reason is False
1
15
b) Both Assertion & Reasoning are correct, Reason is not correct
1
explanation of Assertion
OR
b) Both Assertion & Reasoning are correct, Reason is not correct
explanation of Assertion
16
a) Both Assertion & Reasoning are correct & Reason is the correct
1
explanation of Assertion
17 (i)
b) Tissue respiration
1
(ii)
b) Anaerobic respiration
1
(iii)
1
b) Aerobic
Anaerobic
Amount of energy is high
and consistent in aerobic
and low in anaerobic
(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
1
positive ion
(iii)
a) F
1
(iv)
c) Electronegativity decreases down the group due to increase in atomic
1
radius/ tendency to gain electron decreases.
(v)
d) F and Li are in the same period and across the period atomic
1
2
size/radius decreases from left to right.
19 (i)
b) Convex
1
(ii)
P=1/f
1
P1=1/f1 and P2=1/f2
P1/P2=4/1, hence (1/f1)/(1/f2) = 4/1
Hence f1/f2=1/4
b) ?
(iii)
a) Ratio of height of image to height of object
1
(iv)
m=v/u
1
3=24/u
Hence u = 8cm
c) 8 cm
(v)
c) Not-so-thick lenses would not make the telescope very heavy and
1
they will also allow considerable amount of light to pass through them.
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
2
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.
22
2
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.
3
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
1
milky
1
- 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 1 + 1
element.
? Due to small size of carbon it forms very strong and (or) stable
bonds with other elements
(Any two)
24
i. S>R>P>Q
1
ii. Cu and QSO4
1
25
The phenomenon is called dispersion.
1
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 1
minimum.
26
The overall current needed = 9A. The voltage is 12V
Hence by Ohm's Law V=IR,
2
The resistance for the entire circuit = 12/9 = 4/3 . = R
R1 and R2 are in parallel.
Hence, R=(R1 R2)/(R1 + R2) = 4R2/(4+R2) = 4/3
R2 = 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
3
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).
4
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. 3
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.
29
- Blood passes through filtration units in the kidney called nephron 3
- 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
30
a. Heating of lead nitrate; and electrolysis of acidified water
2
b.
Sunlight
2AgCl(s) 2Ag(s) + Cl2 (g)
1
(No deduction for not mentioning state of reactants and products.)
31
(i) D, As it is on the left side of the table in group 2
1
(ii) C, as it is in the group 18/ Noble gas
1
(iii) E, as we move from left to right across a period, atomic radius 1
decreases
5
32
a.
2
b. Ionic compounds do not conduct electricity in solid state due to 1
absence of free ions but they conduct electricity in molten and
aqueous state due to presence of free ions
33
Refractive index = speed of light in vacuum / speed of light in 1
medium.
Since the refractive index of diamond is more, hence the speed of
light is lesser in diamond.
Let speed of light in water vevw and in diamond bevd.
Refractive index of diamond w.r.t water is say n =
0.5
Speed of light in water / speed of light in diamond.
n = v
w/vd
Dividing both numerator and denominator by speed of light [c] we
get
1
n = (vw/c) ? (vd/c) = Inverse Ratio of refractive index of water and
diamond.
0.5
n= 2.42/1.33 = 1.82 (approx.)
34
? Milk of magnesia 10
2
? Gastric juices 1
? Brine
7
? Aqueous Sodium hydroxide 13
Baking soda undergoes thermal decomposition to form Na2CO3, CO2
and H2O; CO2 makes the cake fluffy & soft
2
Heat
NaHCO3 ?Na2CO3 + CO2 + H2O
Uses
Used in fire extinguishers/ antacid to neutralize excess acid in stomach /
to neutralize the effect of acid in insect sting.
1
6
OR
(i)
a) B
b) C,A,D,B
(ii) Due to moisture in the atmosphere it converted into Gypsum
CaSO4+1? H2O CaSO4.2H2O
5
(iii) Making toys/dolls or statues /fixing broken limbs/making decorative
materials.
35
[Diagram drawn and annotated with the following points will also be
considered ]
5
- Stamen is the male reproductive part and it produces pollen grains.
?The ovary contains ovules and each ovule has an egg cell.
?The pollen needs to be transferred from the stamen to the stigma.
?If this transfer of pollen occurs in the same flower, it is referred to as
self-pollination./ On the other hand, if the pollen is transferred from
one flower to another, it is known as cross-pollination.
After the pollen lands on a suitable stigma, it has to reach the female
germ-cells which are in the ovary. For this, a tube grows out of the
pollen grain and travels through the style to reach the ovary/Figure
?The male germ-cell produced by pollen grain fuses with the female
gamete present in the ovule.
?This fusion of the germ-cells or fertilisation gives the zygote.
?After fertilisation, the zygote divides several times to form an embryo
7
within the ovule.
?The ovule develops a tough coat and is gradually converted into a
seed. The ovary grows rapidly and ripens to form a fruit.
?Meanwhile, the petals, sepals, stamens, style and stigma may shrivel
and fall off.
36
The lamps are in parallel.
1
Advantages:
If one lamp is faulty, it will not affect the working of the other lamps.
1
They will also be using the full potential of the battery as they are
connected in parallel.
The lamp with the highest power will glow the brightest.
1
P=VI
In this case, all the bulbs have the same voltage. But lamp C has the
1
highest current.
Hence, for Lamp C P=5 x 60 Watt = 300 W. (the maximum).
The total current in the circuit = 3+4+5+3 A = 15A
1
The Voltage = 60V
V=IR and hence R = V/I
= 60/15 A = 4A
OR
(i) The magnetic field lines produced is into the plane of the paper
at R and out of it at S.
1
(ii) Field at S > Field at P
Magnetic field strength for a straight current carrying
2
conductor is inversely proportional to the distance from the
wire.
1
(iii) The current will be going from top to bottom in the wire shown
and the magnetic field lines are now in the clockwise direction
on the plane which is perpendicular to the wire carrying
current.
(iv) Right hand thumb rule. The thumb is aligned to the direction
1
of the current and the direction in which the fingers are
wrapped around the wire will give the direction of the
magnetic field.
8
This post was last modified on 07 March 2021