SERIES Z1XYW/2 SET – 3

CBSE-2022-23

Paper: SCIENCE
Date: 04-03-2023 Code: 31/2/3
Max. Marks: 100 Time allowed: 3 hours
Section A
This section has 20 Multiple choice questions (Q.NO. 1 20). Al questions are
compulsory.
1. The number of electrons in the outermost shell of the atom of a non-metal can be :
(a) 1, 2 or 3 (b) 3, 4 or 5 (c) 5, 6 or 7 (d) 5, 6 or 8
Sol. Option (c)
Generally, the atoms of a non-metal contains 5, 6 or 7 valence electrons.
2. Select the correct option(s) in the following table :
Option Natural Sources Acid present
(i) Tamarind Tartaric acid
(ii) Tomato Acetic acid
(iii) Ant sting Oxalic acid
(iv) Nettle sting Methanoic acid
(a) (i) Only (b) (iii) only (c) (i) and (iv) (d) (i), (ii) and (iv)
Sol. Option (c)
(i) and (iv)
Option Natural Sources Acid present
(i) Tamarind Tartaric acid
(ii) Tomato Oxalic acid
(iii) Ant sting Methanoic acid
(iv) Nettle sting Methanoic acid
3. Among the following, the metal with lowest density is :
(a) Lithium (b) Lead (c) Magnesium (d) Aluminium
Sol. Option (a)
Lithium is the metal with lowest density.
4. Which of the following is an example of endothermic process ?
(a) Formation of slaked lime
(b) Decomposition of vegetable matter into compost
(c) Dissolution of ammonium chloride in water
(d) Digestion of food in our body
Sol Option (c)
Ammonium chloride is dissolved in water by absorbing heat, so it’s an endothermic
process.

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5. In order to balance the following chemical equation, the values of the coefficients x and y
respectively are :
Heat
xPb(NO3 )2 ⎯⎯⎯ →2PbO + y NO2 + O2
(a) 2, 4 (b) 2, 2 (c) 2, 3 (d) 4, 2
Sol. Option (a)
2Pb ( NO3 )2 ⎯⎯→
Heat
2PbO + 4NO2 + O2
6. When zinc reacts with sodium hydroxide, the product formed is:
(a) Sodium oxide (b) Sodium zincate (c) Zinc hydroxide (d) Zinc oxide
Sol. Option (b)
When Zinc reacts with sodium hydroxide, sodium zincate is formed with evolution of
hydrogen gas.
7. Select the correct option from the following :
Salt Parent acid Parent base Nature of salt
(a) Sodium acetate CH3COOH NaOH Neutral
(b) Sodium carbonate H2CO3 NaOH Basic
(c) Sodium chloride HCl NaOH Acidic
(d) Sodium nitrate HNO3 NaOH Acidic
Sol. Option (b)
H2CO3 + NaOH → Na2CO3 + H2O
Weak acid Strong base Basic salt Water

8. For verifying ohm's Law, we design an electric circuit diagram in which we show the
arrangement of different circuit components. We find that with respect to the resistor, the:
(a) ammeter is connected in parallel and the voltmeter in series.
(b) ammeter is connected in series and the voltmeter in parallel.
(c) ammeter and voltmeter are both connected in series.
(d) ammeter and voltmeter are both connected in parallel.
Sol. Option (b)
Ammeter is always connected in series because the resistance of an ammeter is very small
due to which it doesn't effect the current to be measured voltmeter is always connected in
parallel because it has very high resistance to ensure that it's connection do not alter how
of current in the circuit.
9. An object is placed in front of a convex mirror at infinity. According to the New Cartesian
Sign Convention, the sign of the focal length and the sign of the image distance in this case
are respectively :
(a) +, – (b) – , + (c) – , – (d) + , +
Sol. Option (d)
As the image formed in a convex mirror is always virtual as well as for the measurement
of focal length again we need to go in the direction of incident ray for the measurement
hence focal length and image distance both are +ve.
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 CBSE BOARD SOLUTIONS (2022-2023)
10. When an ‘X’ bearing sperm fertilizes the egg, the resulting zygote has the following
combination of chromosomes :
(a) 44 + XX (b) 44 + XY (c) 22 + XX (d) 22 + XY
Sol. Option (a)
When an ‘X’ bearing sperm fertilizes the egg, the resulting zygote has 44 + XX combination
of chromosomes.
11. Sphincter muscles are present at the exit of :
(a) Stomach and small intestine
(b) Stomach and anus
(c) Small intestine and large intestine
(d) Oesophagus and stomach
Sol. Option (b)
Sphincter muscles are present at the exit of stomach and anus.
12. In the following diagram, identify the cells through which massive amounts of gaseous
exchange takes place for photosynthesis :

I
II
III

IV
(a) I (b) IV (c) III (d) II
Sol. Option (b)
'IV' as it represents stomata which helps in gaseous exchange.
13. During vigorous exercise, the occurrence of cramps in the outer muscles of an athlete is
due to the conversion of pyruvate to :
(a) Glucose (b) Ethanol (c) Lactic acid (d) Lactose
Sol. Option (c)
During vigorous exercise, the occurrence of cramps in the outer muscles of an athlete is
due to the conversion of pyruvate to lactic acid.
14. Plants which bear unisexual flowers are :
(a) Mustard and Papaya
(b) Hibiscus and Watermelon
(c) Mustard and Hibiscus
(d) Watermelon and Papaya
Sol. Option (d)
Plants which bear unisexual flowers are Watermelon and Papaya.

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15. A positron enters a uniform magnetic field at right angles to it as shown. The direction of
force experienced by the positron will be :
Positron

Magnetic field

(a) to the right (b) to the left (c) into the page (d) out of the page
Sol. Option (c)
By Fleming left hand rule, the direction of force acting on position is found to be into the page.
16. In a resistive circuit if the current is increased to two times, the percentage change in the
amount of heat dissipated in the circuit would be :
(a) 400% (b) 300% (c) 200% (d) 100%
Sol. Option (b)
Heat dissipated is given by
H = I2Rt
If the current is increase to times the original value, then new current given by
H' = I’2Rt = 4I2Rt = 4H
He percentage increases in heat dissipation is given by
4H − H
h% =  100 = 300 %
H

For questions number 17 to 20, two statements are given – one labelled as Assertion
(A) and the other labelled as Reason (R). Select the correct answer to these questions
from the codes (a), (b), (c) and (d) as given below.
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation
of the Assertion (A).
(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct
explanation of the Assertion (A)
(c) Assertion (A) is true, but Reason (R) is false.
(d) Assertion (A) is false, but Reason (R) is true.
17. Assertion (A) : Magnetic field lines do not intersect each other.
Reason (R) : Magnetic field lines are imaginary lines, the tangent to which at any point
gives the direction of the field at that point.
Sol. Option (b)
Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation
of Assertion (A).
Because,
Magnetic field lines are imaginary lines, the tangent drawn at any point gives the direction
of magnetic field at that point, is not the correct explanation of the fact “magnetic field lines
do not intersect each other”, As the needle of the compass can not show deflection in two
different direction at a particular point is the correct explanation of the fact why magnetic
field lines never intersect.
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 CBSE BOARD SOLUTIONS (2022-2023)
18. Assertion (A) : Sodium oxide is an amphoteric oxide.
Reason (R) : Metal oxides which react with both acids as well as bases are known as
amphoteric oxide.
Sol. Option (d) Assertion (A) is false, but Reason (R) is true.
Sodium oxide is a basic oxide.
19. Assertion (A): The angle through which a ray of light bends on passing through a prism
is called the angle of deviation.
Reason (R) : The peculiar shape of a prism makes the emergent ray bend at an angle to
the direction of the incident ray.
Sol. Option (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct
explanation of the Assertion (A).
20. Assertion (A): When a bacterium divides into two, and the resultant two bacteria divide
again, the four bacteria produced would be almost similar.
Reason (R) : DNA copying involves small inaccuracies in the reproduction process.
Sol. Option (b)
Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation
of the Assertion (A).
During asexual reproduction, when a bacterium divides into two and the resultant two
bacteria divide again, the four bacteria produced would be almost similar whereas DNA
copying occurs during sexual reproduction.

SECTION-B

21. V – I graph for two conducting wires A and B are as shown. If both wires are of the same
length and same diameter, which of the two is made of a material of high resistivity ? Give
reasons to justify your answer.

V V
Sol. RB = & RA =
I1 I2
From the graph slope of wire B is greater hence, wire B has greater resistance.
I1 < I2 or RB > RA
R=
A

B  A
A A
B  A

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22. State the role of the following in the process of digestion :
(a) Bile juice and bile salts
(b) Pancreatic enzymes
Sol. (a) Bile juice from the liver makes the food alkaline in addition to acting on fats. Fats are
present in the intestine in the form of large globules which makes it difficult for
enzymes to act on them. Bile salts break them down into smaller globules increasing
the efficiency of enzyme action.
(b) The pancreas secretes pancreatic juice which contains enzymes like trypsin for
digesting proteins and lipase for breaking down emulsified fats.
23. (a) What is observed when aqueous solutions of potassium iodide and lead nitrate are
mixed together ? Name the type of reaction and write the chemical equation for the
reaction that occurs .
OR
(b) When copper powder is heated in a watch glass, a black substance is formed.
(i) Why is this black substance formed ? Name it.
(ii) How can this black substance be reversed to its original form ?
Sol. (a) When aqueous solutions of potassium iodide and lead nitrate are mixed together, a
Yellow precipitate PbI2 is formed along with potassium nitrate solution.
It is a double displacement reaction.
Pb( NO3 )2 (aq) + 2KI(aq) ⎯⎯
→ PbI2(s)  +2KNO3(aq)
OR
(b) (i) The black substance is formed due to the oxidation of copper. The substance
formed is copper oxide [CuO]
(ii) When H2 gas is passed over heated copper oxide (CuO), then the black coloured
CuO is reduced and brown copper metal is obtained back.
CuO + H2 ⎯⎯
→Cu + H2O
24. Mendel crossed a pure tall pea plant (TT) with a pure short pea plant (tt) and obtained all
tall plants in F1 generation.
(a) What is the gene combination present in the plants of F1 generation ?
(b) Give reason why only tall plants are observed in F1 progeny.
(c) What will be the ratio of the plants obtained in the F2 generation when F1 plants are
self-pollinated ?
Sol. (a) All the plants of F1 generation are tall (Tt) ,i.e, heterozygous tall.
(b) In F1 generation, heterozygous tall (Tt) plants were obtained as the Tall (TT) gene was
dominant over dwarf/short (tt) gene.

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 CBSE BOARD SOLUTIONS (2022-2023)
Selfing of F1 plants

Parent Tall Dwarf

(Pure) TT tt Tall Tall
Tt Tt
Male
Gametes
Gametes T t
Female T t
Gametes
TT Tt
T Tall
Fertilization Tall

Tt Tt tt
(All tall) Tall Dwarf
t

F1 Generation F2 Generation

Monohybrid Cross
(c) Ratio of the plants obtained in F2 generation is 1:2:1
25. (a) When and where does a rainbow appear in the sky ? Draw a labelled ray diagram to
show its formation. F2 Generation
OR
(b) What is scattering of light ? Why does the clear sky appear blue ?
Sol. (a) Rainbow formation takes place only if, the sun is at our back, in the presence of tiny
water droplets (Rain drops) in the atmosphere. These droplets acts as small prisms
which makes the sunlight undergo dispersion.
Sunlight
A
R
40° V
42°

Raindrop

OR
(b) Scattering of light is a phenomenon by which a beam of light is redirected in different
directions, when it falls on dust particles, water molecules and the molecules of gases
present in the atmosphere.
Violet, Indigo–Blue color of white light which has the least wavelength among all the
color of light, due to which it scatters the most by the particles of the atmosphere. Hence
the sky appear blue.

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26. "Ozone, although a deadly poison, performs an essential function for the earth and its
inhabitants. "Explain.
Sol. Ozone gas is poisonous in nature. It is formed in atmosphere by the action of ultraviolet
radiation on oxygen gas. The high energy ultraviolet radiation (UV radiation) coming from
the sun splits oxygen gas into free oxygen atoms.
Ultraviolet
O2 ⎯⎯⎯⎯⎯⎯→
radiations from sun
O + O (oxygen atom)
The free oxygen atoms are highly reactive. One oxygen atom reacts with an oxygen
molecule to form an ozone molecule.
O2 + O ⎯⎯→ O3 (Ozone molecule)
The ozone layer is very important for the existence of life on earth because it absorbs most
of the harmful ultraviolet radiation coming from the sun and prevents them from reaching
the earth.

SECTION-C

27. (a) Define oxidation.

(b) Identify the oxidising agent in the following reactions and balance the chemical
equations :
(i) Pb3O4 + HCl → PbCl2 + Cl2 + H2O
(ii) MnO2 + Al → Mn + Al2O3
Sol. (a) Oxidation is a chemical process that takes place when a substance comes into contact
with oxygen or another oxidising substance.
Ex. Rusting of iron.
(b) (i) Pb3O4 + 8HCl → 3PbCl2 + Cl2 + 4H2O
Pb3O4 acts as the oxidising agent.
(ii) 3MnO2 + 4Al → 3Mn + 2Al2O3
MnO2 acts as the oxidising agent.
28. (a) Copper reacts with a moist gas 'A' in the air and slowly loses its shiny brown surface. It
turns green. Identify 'A' and the substance of the green coating formed on the surface
of copper.
(b) How is copper obtained from its sulphide ore ? Write the chemical equations for the
reaction involved in its extraction.
Sol. (a) A → Carbon dioxide gas.
The substance of the green coating formed on the surface of copper is basic copper
carbonate.
(b) Sulphide ore of copper is converted into its oxide simply by roasting. The obtained
oxide is then reduced with carbon or allowed to react with copper sulphide again and
gets reduced.
2Cu2S + 3O2 → 2Cu2O + 2SO2
2Cu2O + Cu2S → 6Cu + SO2
The obtained metal is then purified by electrolytic refining.
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 CBSE BOARD SOLUTIONS (2022-2023)
29. (a) (i) What is meant by excretion ?
(ii) Name the organ that connects the kidneys with the urinary bladder. State its
function.
(iii) List two factors on which the amount of water reabsorbed depends.
OR
(b) (i) In the human respiratory system, name the following :
(I) Part where air is filtered by fine hairs and mucus lining.
(II) Part which separates chest cavity from abdominal cavity.
(III) Balloon like structures where exchange of gases takes place.
(IV) The two large air passages that lead from trachea to the lungs.
(ii) List any two characteristic of lungs which make it an efficient respiratory surface.
Sol. (a) (i) The biological process involved in the removal of these harmful metabolic wastes
from the body is called excretion.
(ii) Ureter connects the kidneys with the urinary bladder Urine produced in the
kidneys passes through the ureters into the urinary bladder.
(iii) The amount of water reabsorbed depends on how much excess water there is in
the body, and on how much of dissolved waste there is to be excreted.
OR
(b) (i) (I) Nostrils (II) Diaphragm (III) Alveoli (IV) Bronchi
(ii) Human lungs are efficient respiratory surfaces because of the thin and large
surface for easy diffusion, moist air sacs with mucus for dissolving the gases. The
air sacs are surrounded by a network of blood capillaries with a good supply of
blood so that more exchange of gases can happen.
30. (a) A student has focussed the image of an object of height 3 cm on a white screen using a
concave mirror of focal length 12 cm. If the distance of the object from the mirror is
18 cm, find the values of the following :
(i) Distance of the image from the mirror
(ii) Height of the image.
OR
(b) Define power of a lens. The focal length of a lens is –10cm. Write the nature of the lens
and find its power. If an object is placed at a distance of 20 cm from the optical centre
of this lens, according to the New Cartesian Sign Convention, what will be the sign of
magnification in this case ?
Sol. (a) ho = +3 cm f = –12 cm u = –18 cm
1 1 1
(i) [v =?] as, = +
f v u
1 1 1 1 1 –1 1 –3 + 2
= − = − == + =
v f u −12 −18 12 18 36
1 –1
= ; [v = –36 cm]
v 36
h −v
(ii) [hI = ?] as, m = I =
ho u
v − ( −36cm )
hI = −  ho =  3cm
u −18cm
[hI = –2 × 3 cm = –6 cm]

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OR
(b) Power of Lens : It is a measure of the degree of convergence or divergence of light ray
falling on it. The power of a lens is defined as the ‘reciprocal of its focal length’.
Given : f = –10 cm = –0.1 m
 1 1 −10 
as, P = = = D = −10D
 f −0.1m 1 
as power is –ve lens is concave lens.
Given : u = –20 cm
For any object distance as we know that the image formed by a concave lens is always
virtual, always gets formed at the same side of the object, hence magnification always
remain positive.
31. Explain how some harmful chemicals enter our bodies through the food chain. Why is the
concentration of these harmful chemicals found to be maximum in human beings ?
Sol. Humans use several types of pesticides and chemicals to protect their crops from diseases
and pests. Chemicals are either washed down into the soil or into the water bodies during
heavy rains. From the soil, these are absorbed by the plants along with water and minerals
and from the water bodies these are taken up by aquatic plants and animals. In this way,
these harmful chemicals enter the food chain. Since these chemicals are non-degradable,
they get accumulated progressively at each trophic level.
Human beings occupy the higher trophic level in a food chain, as these chemicals get
accumulated progressively at each trophic level and harm the human bodies.
32. (a) List two factors on which the magnitude of magnetic field produced by a current
carrying straight conductor depends.
(b) State the rule which determines the direction of magnetic field in the above case.
(c) Draw the pattern of magnetic field lines produced in this case.
Sol. (a) (i) Current in the conductor : The magnitude of the magnetic field produced is
directly proportional to current passing through the wire.
(ii) Distance from the wire : The magnitude of the magnetic field produced is
inversely proportional to the distance from the wire.
(b) Right hand thumb rule : If you imagine holding a current carrying wire in your Right-
Hand with your thumb pointing towards the direction electric current flow then the
direction in which your fingers curls, gives direction of lines of force of the magnetic
field.
Direction
Direction of of
(c) Direction of
magnetic field
Electric current
Direction of
magnetic
Electric field
current

Right hand rule for a current-carrying

circular loop.

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 CBSE BOARD SOLUTIONS (2022-2023)
33. Name the hormone released and the gland which secretes it in human being during scary
situations. How does the body respond to enable it to deal with the situation ?
Sol. Adrenaline is the hormone released by adrenal gland during scary situations.
To enable it to deal with the situation, the body reacts in following ways:
(i) The heart begins to beat faster resulting in supply of more oxygen to the muscles.
(ii) The blood to the digestive system and skin is reduced due to the contraction of
smooth muscles around small arteries in these organs. This diverts the blood to our
skeletal muscles.
(iii) The breathing rate increases because of the contraction of the diaphragm and the rib
muscles.
(iv) All these responses together enable the body to be ready to deal with the situation.

SECTION-D

34. (a) (i) List three points of difference between nervous and hormonal mechanisms for
control and coordination in animals.
(ii) How are auxins related with the bending of plant shoot towards unidirectional
light ? Explain.
(b) (i) Name the disorder which a person is likely to suffer from due to the following :
(I) Over-secretion of growth hormone
(II) Deficiency of oestrogen in females
(III) Less secretion of thyroxine
Also name the gland that secretes each of the hormones mentioned above.
(ii) How is the timing and amount of hormone released regulated ? Explain with the
help of an example.
Sol. (a) (i)
Difference between Nervous and Hormonal Coordination
Nervous Coordination Hormonal Coordination
It is sent as an electrical impulse along It is sent as a chemical messenger via
axons and as a chemical across synapse. blood stream.
Information travels rapidly in milli Information travels slowly.
seconds.
Information is directed to specific Information is spread throughout the
receptors–one or a few nerve fibres, body by blood from which the target
gland cells or other neurons. cells or organs pick it up.
It gets response immediately. It gets response usually slowly.
Its effects are short-lived. Its effects are generally more
prolonged.

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(ii) When growing plants detect light, a hormone called auxin, synthesized at shoot
tip, helps the cells to grow longer.
When light is coming from one side of the plant, auxin diffuses towards the shady
side of the shoot.
This concentration of auxin stimulates the cells to grow longer on the side of the
shoot which is away from light. Thus, the plant appears to bend towards light.

OR
(b) (i)
(I) Growth hormones are released by anterior pituitary gland which regulates the
growth of body. Due to over secretion of growth hormone it leads to gigantism.
(II) Oestrogen hormones are released by ovary in females which causes development
of sexual organs and secondary sexual characteristics in females. Due to
deficiency of oestrogen, menstrual cycle becomes irregular.
(III) Thyroxine is released by thyroid glands. It controls carbohydrate, protein and fat
metabolism. It regulate BMR [Basal metabolic rate]. Due to less secretion it may
cause goitre.
(ii) Feedback mechanism is a
High blood
regulatory mechanism in which Negative Pancreas
glucose
presence of certain level of feedback
substance promotes or inhibits Direct Feedback
its further formation. Hormone
regulation is mostly done by Decreased blood Increased
feedback mechanism. A good glucose Insulin release
example of negative feedback is
the hormone insulin. Insulin is a
hormone produce by the Increased
pancreas. Insulin is released Cellular uptake
when the amount of glucose in of glucose
the blood goes up. It stimulates
Feedback mechanism
the target cells to take glucose
out of the blood which is utilized in cell respiration or is stored as glycogen. When
cells take up glucose from the blood this makes the glucose level normal. With fall
in blood glucose level insulin secretion decreases. This checks the further fall in
blood glucose level. So, the negative feedback work to keep the blood glucose level
normal.

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 CBSE BOARD SOLUTIONS (2022-2023)
35. (a) An acid ‘X’ and an alcohol ‘Y’ react with each other in the presence of an acid catalyst to
form a sweet smelling substance ‘Z’. dentify ‘X’, ‘Y’ and ‘Z’ . Write the chemical equation
for the reaction involved and name it. The substance ‘Z’ on treatment with sodium
hydroxide produces back the alcohol ‘Y’ and sodium ethanoate. Write the chemical
equation of the reaction involved and name it, giving justification for the name.
OR
(b) (i) Name the simplest saturated hydrocarbon. Draw its electron dot structure. Which
type of bonds exist in this compound ?
(ii) Name any two mixtures of the carbon compound used as a fuel in daily life, of
which the above mentioned compound is an important component.
(iii) In which homologous series of carbon compounds can this compound be placed ?
Write the general formula of the series.
(iv) Which type of flame is produced on burning it ?
Sol. (a) X → CH3COOH (Acetic Acid)
Y → C2H5OH (Ethanol)
Z → CH3COOC2H5 (Ethyl acetate)
CH3COOH + C2H5OH ⎯⎯
→CH3COOC2H5 + H2O (Esterification reaction)
x y Z
CH3COOC2H5 + NaOH ⎯⎯
→CH3COONa + C2H5OH
Z y

Above mentioned reaction is known as saponification Reaction.

OR
(b) (i) Methane is the simplest saturated hydrocarbon.
H

x
H x C x H
x

Single covalent bonds exist in methane.

(ii) CH4 (Methane) and C2H6 (Ethane) are mixed to form Natural gas, which is a fuel
in daily life. CH4 is the main component of Natural gas.
(iii) Methane can be placed in homologous series of alkane family.
General formula → CnH2n+2
(iv) Blue coloured flame is produced, when Methane (CH4) gas is burnt.

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36. (a) Draw a ray diagram for showing the convergence of a parallel beam of light by a
concave mirror and mark the positions of pole and the centre of curvature in it.
(b) An object 4 cm in size is placed at 25 cm in front of a concave mirror of focal length
15 cm. At what distance from the mirror should a screen be placed in order to obtain a
sharp image ? Find the nature and size of the image.
(c) List any two uses of a concave mirror.
Sol. (a)

C
F

(b) Given :
Height of an object = 4 cm, Position of object, u = –25 cm
Focal length of mirror, f = –15 cm
From mirror formula
1 1 1 1 1 1
= +  = +
f v u −15 v −25
v = –37.5 cm
− v hi ( −37.5) hi
magnification, m = = =− =
u ho −25 4
hi = −6cm
To get a sharp image v = 37.5 cm
The image is real, inverted and magnified.
(c) (i) Concave mirrors are used as shaving mirrors to see a larger image of the face.
(ii) Concave mirrors are used as reflectors in car head lights, search lights, hand
torches, table lamps, etc. to get powerful parallel beams of light.

SECTION-E
The following questions are source – based / case based questions. Read the case carefully
and answer the questions that follow.
37. The teacher while conducting practical’s in the laboratory divided the students into three
groups and gave them various solutions to find out their pH and classify them into acidic,
basic and neutral solutions.
Group A - Lemon juice, vinegar, colourless aerated drink
Group B - Tomato juice, coffee, ginger juice
Group C - Sodium hydroxide, sodium chloride, lime water
(a) For the solutions provided, which group is / are likely to have pH value (i) less than 7,
and (ii) greater than 7 ?
(b) List two ways of determining pH of a solution
(c) Explain, why the sour substances such as lemon juice are effective in cleaning the
tarnished copper vessels.
OR
(c) “pH has great importance in our daily life.” Justify this statement by giving two
examples.
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 CBSE BOARD SOLUTIONS (2022-2023)
Sol. (a) (i) Group A & Group B are likely to have PH value less than 7.
(ii) Group C is likely to have PH value greater than 7.
(b) (i) By using universal Indicator
(ii) By using Formula PH = –log[H+]
(c) Lemon juice being acidic in nature neutralises basic copper carbonate layer formed on
copper vessel, thus this layer is removed and copper vessel appears with clear shine
again.
OR
(C) (i) Plants and animals are PH sensitive : Living organisms can survive only in narrow
range of PH change.
(ii) PH of the soil : Plants require specific PH range of soil for their normal growth.
38. All the reproductive methods of living organisms are broadly categorized into two types :
1. Asexual reproduction, and 2. Sexual reproduction.
Asexual reproduction involves the participation of a single parent without the formation
of gametes, fertilisation and transfer of genetic material. This method is a common means
of rapidly increasing offsprings under favourable conditions.
(a) Name the type of fission that occurs in Leishmania and Plasmodium.
(b) Write one advantage of sexual mode of reproduction over asexual reproduction.
(c) Give reasons why:
(i) Colonies of yeast fail to multiply in water but multiply in sugar solution.
(ii) Rhizopus individuals do not grow on a dry slice of bread.
OR
(c) Name the filamentous structures a student could identify when he collected water from
a pond that appeared dark green. How do these organisms multiply? Explain.
Sol. (a) Binary fission in Leishmania and multiple fission in Plasmodium.
(b) More genetic variations arises due to sexual reproduction within a species.
Consequently, genetic variations can lead to evolutionary advancement over asexual
reproduction.
(c) (i) Colonies of yeast will multiply in sugar solution because sugar is an organic
molecule which provides energy for all life processes which are essential for
survival.
(ii) In Rhizopus spores are found. These spores are covered by thick walls. For
growing these spores individuals need moist surface and so they can begin to
grow. In absence of moisture or in dry slice of bread, spores would not grow.

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SCIENCE
OR
(c) The filamentous structure observed by the student is of spirogyra.
In this process an organism breaks up into two or more fragments and each fragment
develops into an adult organism. e.g. Spirogyra. This process is called fragmentation.

Spirogyra

Fragmentation in Spirogyra

Spirogyra, simply breaks up into smaller pieces upon maturation which grows into new
individuals.
39. Consider the following electrical circuit diagram in which nine identical resistors of 3
each are connected as shown. If the reading of the ammeter A1 is 1 ampere, answer the
following questions :
+ + 3 +
V1 V2 A2
I2

3 3 3
I1 3 3 + I3
+ A1 A3
P 3 Q 3 R 3 S

+ –
(a) What is the relationship between the readings of A1 and A3 ? Give reasons for your
answer
(b) What is the relationship between the readings of A2 and A3 ?
(c) Determine the reading of the voltmeter V1
OR
(c) Find the total resistance of the circuit.
[16]  Digital
 CBSE BOARD SOLUTIONS (2022-2023)
Sol.
+ – + – 3 +
V1 V2 A2
I2

3 3 3
I1 3 3 + I3
+ A1 – A3
P 3 Q 3 R 3 S

+ –

(a) Readings of [A1 = A3] as RPQ, RQR and RRS are connected in series with the two ammeters
A1 and A3, also we know that in series connection current remain same.
(b) As in equal resistors connected in parallel current remain the same.
1 
Between points PQ in each branch current will remain  A 
2 
1 
Between points QR will remain  A  in each branch and between points RS will
3 
1 
remain  A  in each branch
4 
1 I3
Hence I2 = =
4 4
So, [A3 = 4A2]
 3 
(c)  V1 = VPQ = 1A ( R PQ ) = 1   = 1.5V 
 2 
OR
(c) For the parallel combination shown,
 3   3   3 
 R PQ = 2  ;  R QR = 3 = 1  ;  R RS = 4 
     
3 3 6 + 4 + 3 13 
(R eq = R PQ + R QR + R RS ) =  + 1 + = = 
2 4 4 4 
 13 
R eq = 4  
 

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