Download Central Board of Secondary Education (CBSE) Class 10th (10th Board Exam) Science 2021 Sample Paper
Class X
Science (086) Theory
Time: 3 Hours
Maximum Marks: 80
General Instructions:
(i) The question paper comprises four sections A, B, C and D. There are 36 questions in
the question paper. All questions are compulsory.
(ii) Section?A - question no. 1 to 20 - all questions and parts thereof are of one mark each.
These questions contain multiple choice questions (MCQs), very short answer
questions and assertion - reason type questions. Answers to these should be given in
one word or one sentence.
(iii) Section?B - question no. 21 to 26 are short answer type questions, carrying 2 marks
each. Answers to these questions should in the range of 30 to 50 words.
(iv) Section?C - question no. 27 to 33 are short answer type questions, carrying 3 marks
each. Answers to these questions should in the range of 50 to 80 words.
(v) Section?D ? question no. - 34 to 36 are long answer type questions carrying 5 marks
each. Answer to these questions should be in the range of 80 to 120 words.
(vi) There is no overall choice. However, internal choices have been provided in some
questions. A student has to attempt only one of the alternatives in such questions.
(vii) Wherever necessary, neat and properly labeled diagrams should be drawn.
SECTION A
No.
Questions
Marks
1
List any two observations when Ferrous Sulphate is heated in a dry test tube?
1
OR
Identify the products formed when 1 mL of dil. Hydrochloric acid is added to
1g of Sodium metal?
2
Write the chemical name and chemical formula of the salt used to remove
1
permanent hardness of water.
3
Which of the following is not observed in a homologous series? Give reason
1
for your choice.
a) Change in chemical properties
b) Difference in -CH2 and 14u molecular mass
c) Gradation in physical properties
d) Same functional group
4
Why does the Sun appear white at noon?
1
1
5
Both a spherical mirror and a thin spherical lens have a focal length of (-)15
1
cm. What type of mirror and lens are these?
6
The image formed by a concave mirror is observed to be real, inverted and
1
larger than the object. Where is the object placed?
OR
Name the part of a lens through which a ray of light passes without suffering
any deviation.
7
In the arrangement shown in figure there are two coils wound on a non-
1
conducting cylindrical rod. Initially the key is not inserted in the circuit. Later
the key is inserted and then removed shortly after.
What are the two observations that can be noted from the galvanometer
reading?
8
Draw the magnetic field lines around a straight current carrying conductor.
1
9
Two unequal resistances are connected in parallel. If you are not provided with
1
any other parameters (eg. numerical values of I and R), what can be said about
the voltage drop across the two resistors?
OR
Some work is done to move a charge Q from infinity to a point A in space. The
potential of the point A is given as V. What is the work done to move this
charge from infinity in terms of Q and V?
10
Veins are thin walled and have valves. Justify.
1
11
How is the wall of small intestine adapted for performing the function of
1
absorption of food?
OR
Out of a goat and a tiger, which one will have a longer small intestine? Justify
your answer.
12
Explain how ozone being a deadly poison can still perform an essential
1
function for our environment.
OR
Give reason why a food chain cannot have more than four trophic levels.
2
13
State the role of pancreas in digestion of food.
1
For question numbers 14, 15 and 16, two statements are given- one labeled Assertion (A) and the
other labeled 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.
14
Assertion: After white washing the walls, a shiny white finish on walls is 1
obtained after two to three days.
Reason: Calcium Oxide reacts with Carbon dioxide to form Calcium
Hydrogen Carbonate which gives shiny white finish.
15
Assertion: Food chain is responsible for the entry of harmful chemicals in our 1
bodies.
Reason: The length and complexity of food chains vary greatly.
OR
Assertion: Greater number of individuals are present in lower trophic levels.
Reason: The flow of energy is unidirectional.
16
Assertion: A geneticist crossed a pea plant having violet flowers with a pea 1
plant with white flowers, he got all violet flowers in first generation.
Reason: White colour gene is not passed on to next generation.
Answer Q. No 17 - 20 contain five sub-parts each. You are expected to answer any four sub-
parts in these questions.
17
Read the following and answer any four questions from 17 (i) to 17 (v)
1x4
All living cells require energy for various activities. This energy is available by
the breakdown of simple carbohydrates either using oxygen or without using
oxygen.
(i) Energy in the case of higher plants and animals is obtained by
a) Breathing
b) Tissue respiration
c) Organ respiration
d) Digestion of food
(ii) The graph below represents the blood lactic acid concentration of an athlete
during a race of 400 m and shows a peak at point D.
3
Lactic acid production has occurred in the athlete while running in the 400
m race. Which of the following processes explains this event?
a) Aerobic respiration
b) Anaerobic respiration
c) Fermentation
d) Breathing
(iii) Study the graph below that represents the amount of energy supplied with
respect to the time while an athlete is running at full speed.
Choose the correct combination of plots and justification provided in the
following table.
4
Plot A
Plot B
Justification
a)
Aerobic
Anaerobic
Amount of energy is low and inconsistent
in aerobic and high in anaerobic
b)
Aerobic
Anaerobic
Amount of energy is high and consistent
in aerobic and low in anaerobic
c)
Anaerobic
Aerobic
Amount of energy is high and consistent
in aerobic and low in anaerobic
d)
Anaerobic
Aerobic
Amount of energy is high and inconsistent
in anaerobic and low in aerobic
(iv) The characteristic processes observed in anaerobic respiration are
i) presence of oxygen
ii) release of carbon dioxide
iii) release of energy
iv) release of lactic acid
a) i) ,ii) only
b) i), ii), iii) only
c) ii), iii), iv) only
d) iv) only
(v) Study the table below and select the row that has the incorrect information.
Aerobic
Anaerobic
a)
Location
Cytoplasm
Mitochondria
b)
End Product
CO2 and H20
Ethanol and CO2
c)
Amount of ATP High
Low
d)
Oxygen
Needed
Not needed
18
Read the following and answer any four questions from 18 (i) to 18 (v).
Metallic Character
The ability of an atom to donate electrons and form positive ion (cation) is 1x 4
known as electropositivity or metallic character. Down the group, metallic
character increases due to increase in atomic size and across the period, from
5
left to right electropositivity decreases due to decrease in atomic size.
Non-Metallic Character
The ability of an atom to accept electrons to form a negative ion (anion) is
called non-metallic character or electronegativity. The elements having high
electro-negativity have a higher tendency to gain electrons and form anion.
Down the group, electronegativity decreases due to increase in atomic size and
across the period, from left to right electronegativity increases due to decrease
in atomic size.
18 (i) Which of the following correctly represents the decreasing order of metallic
character of Alkali metals plotted in the graph?
a) Cs>Rb>Li>Na>K
b) K>Rb>Li>Na>Cs
c) Cs>Rb>K>Na>Li
d) Cs>K>Rb>Na>Li
18 (ii) Hydrogen is placed along with Alkali metals in the modern periodic table
though it shows non-metallic character
a) as Hydrogen has one electron & readily loses electron to form negative
ion
b) as Hydrogen can easily lose one electron like alkali metals to form
positive ion
c) as Hydrogen can gain one electron easily like Halogens to form
negative ion
d) as Hydrogen shows the properties of non-metals
18 (iii) Which of the following has highest electronegativity?
a) F
b) Cl
c) Br
d) I
6
18 (iv) Identify the reason for the gradual change in electronegativity in halogens
down the group.
a) Electronegativity increases down the group due to decrease in atomic
size
b) Electronegativity decreases down the group due to decrease in
tendency to lose electrons
c) Electronegativity decreases down the group due to increase in atomic
radius/ tendency to gain electron decreases
d) Electronegativity increases down the group due to increase in forces of
attractions between nucleus & valence electrons
18 (v) Which of the following reason correctly justifies that "Fluorine (72pm) has
smaller atomic radius than Lithium (152pm)"?
a) F and Li are in the same group. Atomic size increases down the group
b) F and Li are in the same period. Atomic size increases across the
period due to increase in number of shells
c) F and Li are in the same group. Atomic size decreases down the group
d) F and Li are in the same period and across the period atomic size/radius
decreases from left to right.
19
Read the following and answer any four questions from 19 (i) to 19 (v)
Sumati wanted to see the stars of the night sky. She knows that she needs a
telescope to see those distant stars. She finds out that the telescopes, which are 1x 4
made of lenses, are called refracting telescopes and the ones which are made of
mirrors are called reflecting telescopes.
So she decided to make a refracting telescope. She bought two lenses, L1 and
L2. out of which L1 was bigger and L2 was smaller. The larger lens gathers and
bends the light, while the smaller lens magnifies the image. Big, thick lenses
are more powerful. So to see far away, she needed a big powerful lens.
Unfortunately, she realized that a big lens is very heavy.
Heavy lenses are hard to make and difficult to hold in the right place. Also
7
since the light is passing through the lens, the surface of the lens has to be
extremely smooth. Any flaws in the lens will change the image. It would be
like looking through a dirty window.
19 (i) Based on the diagram shown, what kind of lenses would Sumati need to make
the telescope?
a) Concave lenses
b) Convex lenses
c) Bifocal lenses
d) Flat lenses
19 (ii) If the powers of the lenses L1 and L2 are in the ratio of 4:1, what would be the
ratio of the focal length of L1 and L2?
a) 4:1
b) 1:4
c) 2:1
d) 1:1
19 (iii) What is the formula for magnification obtained with a lens?
a) Ratio of height of image to height of object
b) Double the focal length.
c) Inverse of the radius of curvature.
d) Inverse of the object distance.
19 (iv) Sumati did some preliminary experiment with the lenses and found out that the
magnification of the eyepiece (L2) is 3. If in her experiment with L2 she found
an image at 24 cm from the lens, at what distance did she put the object?
a) 72 cm
b) 12 cm
c) 8 cm
d) 6 cm
19 (v) Sumati bought not-so-thick lenses for the telescope and polished them. What
advantages, if any, would she have with her choice of lenses?
a) She will not have any advantage as even thicker lenses would give
clearer images.
b) Thicker lenses would have made the telescope easier to handle.
c) Not-so-thick lenses would not make the telescope very heavy and also
allow considerable amount of light to pass.
d) Not-so-thick lenses will give her more magnification.
8
20
Read the following and answer any 4 questions from 20 (i) to 20 (v).
4
A solenoid is a long helical coil of wire through which a current is run in
order to create a magnetic field. The magnetic field of the solenoid is the
superposition of the fields due to the current through each coil. It is nearly
uniform inside the solenoid and close to zero outside and is similar to the field
of a bar magnet having a north pole at one end and a south pole at the other
depending upon the direction of current flow. The magnetic field produced in
the solenoid is dependent on a few factors such as, the current in the coil,
number of turns per unit length etc.
The following graph is obtained by a researcher while doing an experiment to
see the variation of the magnetic field with respect to the current in the
solenoid.
The unit of magnetic field as given in the graph attached is in milli-Tesla (mT)
and the current is given in Ampere.
20 (i) What type of energy conversion is observed in a linear solenoid?
a. Mechanical to Magnetic
b. Electrical to Magnetic
c. Electrical to Mechanical
d. Magnetic to Mechanical
20 (ii) What will happen if a soft iron bar is placed inside the solenoid?
a. The bar will be electrocuted resulting in short-circuit.
b. The bar will be magnetised as long as there is current in the circuit.
c. The bar will be magnetised permanently.
d. The bar will not be affected by any means.
20 (iii) The magnetic field lines produced inside the solenoid are similar to that of ...
a. a bar magnet
9
b. a straight current carrying conductor
c. a circular current carrying loop
d. electromagnet of any shape
20 (iv) After analysing the graph a student writes the following statements.
I.
The magnetic field produced by the solenoid is inversely proportional
to the current.
II.
The magnetic field produced by the solenoid is directly proportional to
the current.
III.
The magnetic field produced by the solenoid is directly proportional to
square of the current.
IV.
The magnetic field produced by the solenoid is independent of the
current.
Choose from the following which of the following would be the correct
statement(s).
a. Only IV
b. I and III and IV
c. I and II
d. Only II
20 (v) From the graph deduce which of the following statements is correct.
a. For a current of 0.8A the magnetic field is 13 mT
b. For larger currents, the magnetic field increases non-linearly.
c. For a current of 0.8A the magnetic field is 1.3 mT
d. There is not enough information to find the magnetic field
corresponding to 0.8A current.
SECTION B
21
Bile juice does not have any digestive enzyme but still plays a significant role
2
in the process of digestion. Justify the statement.
OR
In birds and mammals the left and right side of the heart are separated. Give
reasons.
22
State the events occurring during the process of photosynthesis. Is it essential
2
that these steps take place one after the other immediately?
23
Give a test that can be used to confirm the presence of carbon in a compound.
2
With a valency of 4, how is carbon able to attain noble gas configuration in its
compounds?
OR
The number of carbon compounds is more than those formed by all other
elements put together. Justify the statement by giving two reasons.
10
24
The following observations were made by a student on treating four metals P,
2
Q, R and S with the given salt solutions:
Sample MgSO4(aq)
Zn(NO3)2(aq) CaSO4(aq)
Na2SO4(aq)
P
No reaction
Reaction
Reaction
No reaction
occurs
occurs
Q
Reaction
Reaction
Reaction
Reaction
occurs
occurs
occurs
occurs
R
No Reaction Reaction
No Reaction
No Reaction
Occurs
S
No Reaction
No Reaction
No Reaction
No Reaction
Based on the above observations:
(a) Arrange the given samples in the increasing order of reactivity
(b) Write the chemical formulae of products formed when Q reacts with
CuSO4 solution.
25
A student observes the above phenomenon in the lab as a white light passes
through a prism. Among many other colours, he observed the position of the
two colours Red and Violet.
2
What is the phenomenon called? What is the reason for the violet light to bend
more than the red light?
11
26
2
A student has two resistors- 2 and 3 . She has to put one of them in place
of R2 as shown in the circuit. The current that she needs in the entire circuit is
exactly 9A. Show by calculation which of the two resistors she should choose.
Section C
27
After self-pollination in pea plants with round, yellow seeds, following types
3
of seeds were obtained by Mendel:
Seeds
Number
Round, yellow
630
Round, green
216
Wrinkled, yellow
202
Wrinkled, green
64
Analyse the result and describe the mechanism of inheritance which explains
these results.
OR
In humans, there is a 50% probability of the birth of a boy and 50 %
probability that a girl will be born. Justify the statement on the basis of the
mechanism of sex-determination in human beings.
28
Plastic cups were used to serve tea in trains in early days- these could be
3
returned to the vendors, cleaned and reused. Later,Kulhads were used instead
of plastic cups. Now, paper cups are used for serving tea.
What are the reasons for the shift from Plastic to Kulhads and then finally to
paper cups?
29
Explain where and how urine is produced?
3
12
30
a. Which of the following reactions is/ are an endothermic reaction(s) where
3
decomposition also happens?
? Respiration
? Heating of lead nitrate
? Decomposition of organic matter
? Electrolysis of acidified water
b. Silver chloride when kept in the open turns grey. Illustrate this with a
balanced chemical equation.
31
The following table shows the position of five elements A, B, C, D and E in
3
the modern periodic table.
Group 1
2
3 to 12 13 14 15
16
17
18
Period
2
A
B
C
3
D
E
Answer the following giving reasons:
(i) Which element is a metal with valency two?
(ii) Which element is least reactive?
(iii) Out of D and E which element has a smaller atomic radius?
32
a. Explain the formation of Calcium Chloride with the help of electron dot
3
structure. (At numbers: Ca = 20; Cl = 17)
b. Why do ionic compounds not conduct electricity in solid state but conduct
electricity in molten and aqueous state?
33
Refractive index of water with respect to air is 1.33 and that of diamond is
3
2.42.
(i) In which medium does the light move faster, water or diamond?
(ii) What is the refractive index of diamond with respect to water?
Section D
34
Match the following pH values 1, 7, 10, 13 to the solutions given below:
5
? Milk of magnesia
? Gastric juices
? Brine
? Aqueous Sodium hydroxide.
Amit and Rita decided to bake a cake and added baking soda to the cake batter.
13
Explain with a balanced reaction, the role of the baking soda. Mention any
other use of baking soda.
OR
(i) Four samples A, B, C and D change the colour of pH paper or solution to
Green, Reddish-pink, Blue and Orange. Their pH was recorded as 7, 2, 10.5 &
6 respectively. Which of the samples has the highest amount of Hydrogen ion
concentration? Arrange the four samples in the decreasing order of their pH.
(ii) Rahul found that the Plaster of Paris, which he stored in a container, has
become very hard and lost its binding nature. What is the reason for this? Al-
so, write a chemical equation to represent the reaction taking place.
(iii) Give any one use of Plaster of Paris other than for plastering or
smoothening of walls.
35
Trace the changes that take place in a flower from gamete formation to fruit
5
formation.
36
In the given circuit, A, B, C and D are four lamps connected with a battery of
5
60V.
Analyse the circuit to answer the following questions.
(i) What kind of combination are the lamps arranged in (series or parallel)?
(ii) Explain with reference to your above answer, what are the advantages (any
two) of this combination of lamps?
(iii) Explain with proper calculations which lamp glows the brightest?
(iv) Find out the total resistance of the circuit.
OR
PQ is a current carrying conductor in the plane of the paper as shown in the
figure below.
14
(i) Find the directions of the magnetic fields produced by it at points R and S?
(ii) Given r1> r2, where will the strength of the magnetic field be larger? Give
reasons.
(iii) If the polarity of the battery connected to the wire is reversed, how would
the direction of the magnetic field be changed?
(iv) Explain the rule that is used to find the direction of the magnetic field for a
straight current carrying conductor.
15
This post was last modified on 07 March 2021