Solved 2024 Sample Question Paper CBSE Class 10 Science

Section A (Objective Type Questions 1 Mark Each)

Question 1

Identify the product which represents the solid state in the below reaction.

1. Barium chloride
2. Barium sulphate
3. Sodium chloride
4. Sodium sulphate

Answer

Barium sulphate

Reason — When sodium sulphate is reacted with barium chloride, a white ppt. of barium sulphate is produced.

Na₂SO₄ (aq) + BaCl₂ (aq) ⟶ BaSO₄ (s) + 2NaCl (aq)

Question 2

The colour of the solution observed after 30 minutes of placing zinc metal to copper sulphate solution is

1. Blue
2. Colourless
3. Dirty green
4. Reddish Brown

Answer

Colourless

Reason — Zinc due to its high reactivity displaces copper from copper sulphate and forms zinc sulphate and thus copper gets deposited and the blue coloured solution becomes colourless.

Zn + CuSO₄ ⟶ Cu + ZnSO₄

Question 3

Mild non-corrosive basic salt is

1. Ca(OH)₂
2. NaCl
3. NaOH
4. NaHCO₃

Answer

NaHCO₃

Reason — Sodium hydrogen carbonate [NaHCO₃] is a mild non-corrosive basic salt.

Question 4

On adding dilute sulphuric acid to a test tube containing a metal 'X', a colourless gas is produced when a burning match stick is brought near it. Which of the following correctly represents metal 'X'?

1. Sodium
2. Sulphur
3. Copper
4. Silver

Answer

Sodium

Reason — When sodium is reacted with dil. H₂SO₄, sodium sulphate is formed and hydrogen gas is liberated.

2Na + H₂SO₄ (dil.) ⟶ Na₂SO₄ + H₂

Question 5

Which one of the following correctly represents Sodium oxide?

Answer

Reason — The valency of sodium is 1 and that of oxygen is -2. Two sodium cations and one oxygen anion form an ionic bond and the chemical formula of sodium oxide is Na₂O.

Question 6

An element with atomic number ............... will form a basic oxide.

1. 7 (2,5)
2. 17 (2,8,7)
3. 14 (2,8,4)
4. 11 (2,8,1)

Answer

11 (2,8,1)

Reason — Metals form basic oxides with 1 to 3 electrons in their outermost shell, whereas non-metals form acidic oxides with 4 to 8 electrons in their outermost shell.

Question 7

An element 'M' has 50% of the electrons filled in the 3rd shell as in the 2nd shell. The atomic number of 'M' is:

1. 10
2. 12
3. 14
4. 18

Answer

14

Reason — Electrons are in third shell, so, first and second shells must be completely filled i.e., they have 2 and 8 electrons. Now, as third shell has half of second shell, so, there will be 4 electrons in the third shell.

Hence, 'M' will have 2+8+4 = 14 electrons.

Question 8

Generally food is broken and absorbed within the body of organisms. In which of the following organisms is it done outside the body?

1. Amoeba
2. Mushroom
3. Paramoecium
4. Lice

Answer

Mushroom

Reason — Mushroom as well as all other Fungi show extracellular digestion. Their cell wall release enzymes which digest the food outside their body and the digested food is then absorbed.

Question 9

Receptors are usually located in sense organs. Gustatory receptors are present in

1. tongue
2. nose
3. eye
4. ear

Answer

tongue

Reason — Gustatory receptors are present in taste buds of tongue. They perceive taste of food.

Question 10

A farmer wants to grow banana plants genetically similar enough to the plants already available in his field. Which one of the following methods would you suggest for this purpose?

1. Regeneration
2. Budding
3. Vegetative propagation
4. Sexual reproduction

Answer

Vegetative propagation

Reason — Banana is reproduced by vegetative method (rhizomes). Resulting plants are identical to mother plant.

Question 11

Height of a plant is regulated by:

1. DNA which is directly influenced by growth hormone.
2. Genes which regulate the proteins directly.
3. Growth hormones under the influence of the enzymes coded by a gene.
4. Growth hormones directly under the influence of a gene.

Answer

Growth hormones under the influence of the enzymes coded by a gene.

Reason — Genes code for enzymes that influence the synthesis and regulation of growth hormones, ultimately determining the plant's overall growth and height.

Question 12

A sportsman, after a long break of his routine exercise, suffered muscular cramps during a heavy exercise session. This happened due to:

1. lack of carbon dioxide and formation of pyruvate.
2. presence of oxygen and formation of ethanol.
3. lack of oxygen and formation of lactic acid.
4. lack of oxygen and formation of carbon dioxide.

Answer

lack of oxygen and formation of lactic acid.

Reason — Muscular cramps during heavy exercise are often associated with the accumulation of lactic acid in muscles. This occurs when there is insufficient oxygen available to meet the energy demands of the muscles, leading to anaerobic metabolism and the production of lactic acid.

Question 13

An object is placed in front of a convex mirror. Its image is formed :

1. at a distance equal to the object distance in front of the mirror.
2. at twice the distance of the object in front of the mirror.
3. half the distance of the object in front of the mirror.
4. behind the mirror and it's position varies according to the object distance.

Answer

behind the mirror and it's position varies according to the object distance.

Reason — When an object is placed in front of a convex mirror, its image is formed behind the mirror and it's position varies according to the object distance.

Question 14

When light enters the atmosphere it strikes on extremely fine particles, which deflect the rays of light in all possible directions, This is due to -

1. reflection of light
2. atmospheric refraction
3. scattering of light
4. dispersion of light

Answer

scattering of light

Reason — When light enters the atmosphere it strikes on extremely fine particles, which deflect the rays of light in all possible directions, This is due to scattering of light.

Question 15

In 1987, an agreement was formulated by the United Nations Environment Programme (UNEP) to freeze the production of “X” to prevent depletion of “Y”. “X” and “Y” respectively referred here are:

1. Ozone; CFCs
2. CFCs; rays UV
3. CFCs; Ozone
4. UV rays; Diatomic oxygen

Answer

CFCs, Ozone

Reason — In 1987, an agreement was formulated by the United Nations Environment Programme (UNEP) to freeze the production of CFCs to prevent the depletion of Ozone.

Question 16

Which of the following features relates to biodegradable substances?

1. Broken down by biological processes
2. Remain inert
3. Persist in environment for long time
4. May harm the ecosystem

Answer

Broken down by biological processes

Reason — Biodegradable substances are the substance that degrade or decompose naturally by the action of microorganisms.

Question 17

Assertion: Rusting of Iron is endothermic in nature.

Reason: As the reaction is slow, the release of heat is barely evident.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, and R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

A is false but R is true

Reason — Rusting of iron is an exothermic process. It is a slow process and the amount of heat released isn't significant per unit of time.

Question 18

Assertion: Probability of survival of an organism produced through sexual reproduction is more than that of organism produced through asexual mode.

Reason: Variations provide advantages to individuals for survival.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, and R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true, and R is the correct explanation of A.

Reason — Variations help individual to adapt to the changes in the environment and hence increases the chance of survival.

Question 19

Assertion : A compass needle is placed near a current carrying wire. The deflection of the compass needle decreases when the magnitude of the current in the wire is increased.

Reason : The strength of a magnetic field at a point near the conductor increases on increasing the current.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, and R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

A is false but R is true.

Reason — A compass needle is placed near a current carrying wire. The deflection of the compass needle increases when the magnitude of the current in the wire is increased because strength of a magnetic field at a point near the conductor increases on increasing the current.

Question 20

Assertion: Biodegradable substances result in the formation of compost and natural replenishment.

Reason: It is due to breakdown of complex inorganic substances into simple organic substances.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, and R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

A is true but R is false.

Reason — Biodegradable substances result in the formation of compost and natural replenishment due to breakdown of complex organic substances into simple organic substances.

Section B (Very Short Answer Questions 2 Marks Each)

Question 21

Dil. HCl is added to Zn granules. How will you prove that chemical change has taken place here? Support your response with two arguments.

Answer

Two arguments in support of chemical change in this case are:

1. Change in colour — Zinc metal displaces hydrogen gas and a new black coloured product zinc chloride is formed.
2. Evolution of gas — Bubbles are seen which shows a gas (hydrogen gas) is released.

Question 22

State the post-fertilisation changes that lead to fruit formation in plants.

Answer

After fertilisation, the zygote divides several times to form an embryo within the ovule. The ovule develops a tough coat (seed coat) and is gradually converted into a seed. The ovary grows rapidly and ripens to form a fruit. The petals, sepals, stamens, style and stigma may shrivel and fall off.

Question 23(a)

What is the purpose of making urine in the human body? Name the organs that stores and releases the urine.

Answer

The purpose of making urine in the human body is to filter out nitrogenous waste products i.e. urea and uric acid from the blood. The organ that stores urine is urinary bladder and organ that releases urine is urethra.

Question 23(b)

Why do arteries have thick and elastic walls whereas veins have valves?

Answer

The blood emerges from the heart under high pressure and flows through arteries. The walls of arteries are thick and elastic to bear the pressure. The veins have valves to avoid back-flow of blood and ensure unidirectional flow of blood.

Question 24

The refractive indices of three media are given below:

A ray of light is travelling from A to B and another ray is travelling from B to C.

(a) In which of the two cases the refracted ray bends towards the normal?

(b) In which case does the speed of light increase in the second medium? Give reasons for your answer.

Answer

(a) The light ray travelling from A to B will bend towards the normal because when a ray of light travels from optically rarer medium to an optically denser medium it moves towards the normal and in this case as n_B > n_A so, A is a rarer medium and B is a denser medium.

(b) Speed of light increases in the second medium when light travels from B to C. Since speed of light is inversely proportional to refractive index and n_B > n_C so its speed increases when travelling from B to C.

Question 25(a)

A piece of wire of resistance R is cut into three equal parts. These parts are then connected in parallel. If the equivalent resistance of this parallel combination is R₁, what is the value of the ratio R₁ : R?

Answer

Given,

Wire of resistance R is cut into three parts so resistance of each part = $\dfrac{\text{R}}{3}$ Ω. [∵ resistance is proportional to the length of the wire]

3 wires of resistance $\dfrac{\text{R}}{3}$ Ω are connected in parallel and its equivalent resistance = R₁ Ω

So, $\dfrac{1}{\text{R}_1}$ = $\dfrac{3}{\text{R}}$ + $\dfrac{3}{\text{R}}$ + $\dfrac{3}{\text{R}}$ = $\dfrac{9}{\text{R}}$ Ω

Hence, R₁ = $\dfrac{\text{R}}{9}$

Ratio of R₁ : R = ?

$\dfrac{\text{R}_1}{\text{R}} = \dfrac{\dfrac{\text{R}}{9}}{\text{R}} \\[1em] = \dfrac{\text{R}}{9 \times R} \\[1em] = \dfrac{1}{9}$

∴ Ratio R₁ : R = $\dfrac{1}{9}$

Question 25(b)

Refer to the image below and state how the magnetic field pattern indicates regions where the magnetic field is stronger outside the magnet? What happens to the magnetic field when the current in the circuit is reversed?

Answer

The magnetic field strength is more in the region where the field lines are crowded. This indicates that the field strength is maximum near the poles and it reduces as we go away from the poles.

When the direction of current in the circuit is reversed the direction of the magnetic field is also reversed.

Question 26

Study the food chain given below and answer the questions that follow

(a) If the amount of energy available at the third trophic level is 100 joules, then how much energy will be available at the producer level? Justify your answer.

(b) Is it possible to have 2 more trophic levels in this food chain just before the fourth trophic level? Justify your answer.

Answer

(a) According to the rule of flow of energy, 10% of energy is available for the next trophic level. Therefore, 10000 J of energy will be available at producer level if the amount of energy available at the third trophic level is 100 joules.

(b) No, it is not possible to have 2 more trophic levels in this food chain just before the fourth trophic level because the loss of energy at each step is so great that very little usable energy will remain after 4 trophic levels.

Section C (Short Answer Questions 3 Marks Each)

Question 27

The given reaction shows one of the processes to extract the metals like Iron and Manganese.

MnO₂ (s) + Al(s) ⟶ Mn(l) + Al₂O₃(s) + Heat

(a) Give reason why the above reaction is known as a thermite reaction.

(b) Identify the substance oxidised and reduced in the above reaction.

(c) Give a reason why Aluminium is preferably used in thermite reactions.

Answer

(a) The reaction is known as thermite reaction because the amount of heat evolved is very large due to which the metal (Mn) produced is in molten state.

(b) Al is oxidised and forms Al₂O₃
     MnO₂ is reduced to Mn

(c) Aluminium is highly reactive and is placed above Fe and Mn in the reactivity series. Hence, it reduces MnO₂ to Mn and Fe₂O₃ to Fe and is used in thermite reactions.

Question 28(a)

An element 'M' with electronic configuration 2 8 3 combines separately with Cl^-, SO₄^-2 anions. Write the chemical formulae of the compounds formed. Predict with the suitable reason the nature of the bond formed by element 'M' in general. How will the electrical conductivity of the compounds formed vary with respect to 'M'?

Answer

(i) Given, electronic configuration of M is 2, 8, 3. Hence, its valency is +3.

When M and Cl^- combine

Chemical formula of iron (III) sulphate:

$\text{M}^{3+} \space \text{Cl}^{1-} \\[1em] \overset{\phantom{22}{3}}{\text{M}} \space {\swarrow}\mathllap{\searrow} \space \overset{1}{\text{Cl}} \Rightarrow \underset{\phantom{2}{1}}{\text{M}} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{2}{3}}{\text{Cl}} \\[1em] \text{MCl}_3$

∴ Chemical formula will be MCl₃

(ii) When M and SO₄^-2 combine

$\text{M}^{3+} \space \text{SO}_4^{2-} \\[1em] \overset{\phantom{22}{3}}{\text{M}} \space {\swarrow}\mathllap{\searrow} \space \overset{2}{\text{SO}_4} \Rightarrow \underset{\phantom{2}{2}}{\text{M}} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{2}{3}}{\text{SO}_4} \\[1em] \text{M}_2\text{(SO}_4)_3$

∴ Chemical formula will be M₂(SO₄)₃

M in general forms Ionic bond because it acquires a stable electronic configuration of neon (2, 8) by losing its three valence electrons to form M³⁺ cation.

Compounds of M will be ionic compounds so they will conduct electricity in liquid or molten state only but not in solid state. Element 'M' on the other hand can conduct electricity in solid state due to the presence of 3 free electrons in its outermost shell.

Question 28(b)

A reddish-brown metal 'X', when heated in air, gives a black compound 'Y', which when heated in presence of H₂ gas gives 'X' back. 'X' is refined by the process of electrolysis; this refined form of 'X' is used in electrical wiring.

Identify 'X' and 'Y'. Draw a well-labeled diagram to represent the process of refining 'X'.

Answer

X is Copper [Cu] and in presence of oxygen it forms Y i.e., Copper oxide [CuO].

2Cu + O₂ ⟶ 2CuO

Question 29

We are advised to take iodised salt in our diet by doctors. Justify it's importance in our body.

Answer

We are advised to take iodised salt in our diet by doctors because Iodine is essential for the synthesis of thyroxin hormone. Thyroxin regulates carbohydrate, protein and fat metabolism in the body. Iodised salt prevents goitre/thyroid disease. It provides balanced growth in the body.

Question 30

What is the probability of a girl or a boy being born in a family? Justify your answer.

Answer

There are 50% chances that a girl may be born and 50% chances that a boy may be born. It can be explained as follows:

Most human chromosomes have a maternal copy and a paternal copy. We have 22 such chromosomes. One pair of chromosomes called sex chromosomes is odd in not always being a perfect pair. Women have a perfect pair of sex chromosomes, both called X. But men have a mismatched pair of sex chromosomes in which one is normal sized X chromosome while the other is a short one called Y chromosome. A child receives one chromosome from mother which is essentially X chromosome. 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.

Question 31

(i) Explain why the refractive index of any material with respect to air is always greater 1.

(ii) In the figure below a light ray travels from air into the semi-circular plastic block. Give a reason why the ray does not deviate at the semi-circular boundary of the plastic block.

(iii) Complete the ray diagram of the above scenario when the light ray comes out of the plastic block from the top flat end.

Answer

(i) The refractive index of a medium with respect to air is given by $\dfrac{\text{Speed of light in air}}{\text{Speed of light in the medium}}$.

As speed of light in the medium is always less than the speed of light in air, hence, the above ratio is always greater than one.

(ii) The ray enters the plastic block along the normal (perpendicular) to the surface and for normal incidence there is no deviation. Hence, the ray of light does not deviate at the semi-circular boundary of the plastic block.

(iii) Completed ray diagram of the light ray coming out of the plastic block from the top flat end is shown below:

Question 32

(i) State the law that explains the heating effect of current with respect to the measurable properties in an electrical circuit.

(ii) List the factors on which the resistance of a conductor depends.

Answer

(i) Joules law of heating states that the heat dissipated across a resistor is directly proportional to

1. the square of the current flowing through it
2. resistance of the conductor
3. duration of flow of current

i.e., H = I²Rt

(ii) Resistance of conductor depends on —

1. length of the conductor — the resistance of a conductor is directly proportional to the length of the conductor.
   R ∝ l
2. area of cross section — the resistance of a conductor is inversely proportional to it's area of cross section (a) normal to the direction of flow of current.
   R ∝ $\dfrac{1}{a}$
3. temperature of the conductor — the resistance of conductor increases with an increase in it's temperature.
4. nature of material.

Question 33

Anannya responded to the question: Why do electrical appliances with metallic bodies are connected to the mains through a three pin plug, whereas an electric bulb can be connected with a two pin plug?

She wrote: Three pin connections reduce heating of connecting wires.

(i) Is her answer correct or incorrect? Justify.

(ii) What is the function of a fuse in a domestic circuit?

Answer

(i) Anannya's answer is wrong. Electrical appliances with metallic bodies need an earth wire which provides a low resistance conducting path to the flow of current in the case when there is an accidental leakage of current through the conducting body of the appliances.

(ii) An electric fuse safeguards the circuit and appliances connected in the circuit from being damaged if the current in the circuit exceeds the specified value due to voltage fluctuations or short circuiting. An important component of an electrical fuse is a metal wire or strip that melts when excess current flows through it.

Section D (Long Answer Questions 5 Marks Each)

Question 34(a)

(a) Rehmat classified the reaction between Methane and Chlorine in presence of sunlight as a substitution reaction. Support Rehmat's view with suitable justification and illustrate the reaction with the help of a balanced chemical equation.

(b) Chlorine gas was prepared using electrolysis of brine solution. Write the chemical equation to represent the change. Identify the other products formed in the process and give one application of each.

Answer

(a) Rehmat's observation is correct as the hydrogen atoms are substituted by hetero atom i.e., Cl

CH₄ + Cl₂ ${\xrightarrow{\text{In presence of sunlight}}}$ CH₃Cl + HCl

(b) 2NaCl (aq) + 2H₂O (l) ⟶ 2NaOH (aq) + Cl₂ (g) + H₂ (g)

• NaCl ⟶ Na⁺ + Cl^-

• 2Cl^- ⟶ Cl₂ + 2e^- [At anode]

• H₂O ⟶ H⁺ + OH^-

• 2H⁺ + 2e^- ⟶ H₂ [At cathode]

• Na⁺ + OH^- ⟶ NaOH

Other products formed are sodium hydroxide and hydrogen gas.

Uses of Sodium hydroxide:

• Degreasing of metals
• Preparation of soaps and detergents
• Paper making
• Artificial fibres

Uses of Hydrogen:

• Fuel
• Hydrogenation of vegetable oil to make vanaspati ghee
• Manufacture of ammonia for fertilizer

Question 34(b)

Raina while doing certain reactions observed that heating of substance 'X' with vinegar like smell with a substance 'Y' (which is used as an industrial solvent) in presence of conc. Sulphuric acid on a water bath gives a sweet-smelling liquid 'Z' having molecular formula C₄H₈O₂. When heated with caustic soda (NaOH), 'Z' gives back the sodium salt of and the compound 'Y'. Identify 'X', 'Y', and 'Z'. Illustrate the changes with the help of suitable chemical equations.

Answer

X — Ethanoic acid/ acetic acid/ CH₃COOH [vinegar like smell]

Y — Ethanol/ Ethyl alcohol/ C₂H₅OH [industrial solvent]

Z — Ethyl ethanoate/ Ester – CH₃COOC₂H₅ [sweet-smelling liquid]

CH₃COOH + C₂H₅OH ${\xrightarrow{\text{Conc sulphuric acid}}}$ CH₃COOC₂H₅ + H₂O

CH₃COOC₂H₅ ${\xrightarrow{\text{NaoH}}}$ C₂H₅OH + CH₃COONa

Question 35(a)

Given below are certain situations. Analyze and describe its possible impact on a person:

a) Testes of a male boy are not able to descend into scrotum during his embryonic development.

b) Vas deferens of a man is plugged.

c) Prostate and seminal vesicles are not functional.

d) Egg is not fertilised in a human female.

e) Placenta does not attach to the uterus optimally.

Answer

a) An abnormal condition results when testes of a male boy do not descend into scrotum during his embryonic development and it leads to sterility i.e., incapability to produce sperms as sperm formation requires a lower temperature than the body temperature.

b) Vas deferens is a passage for transfer of sperms, so sperms will not be transferred further if it is plugged. This is known as vasectomy and is a surgical birth control method for males.

c) When prostate and seminal vesicles are not functional, they will not add secretions for nourishment and medium for the transport of sperms.

d) When an egg is not fertilised in a human female, it lives for about one day. Then, the thickened lining of the uterus breaks leading to discharge of blood and mucus along with the unfertilised egg. This is called menstruation.

e) If placenta does not attach to the uterus optimally, nutrition and oxygen will not be provided to the growing embryo affecting its growth, which could have serious implications on development of the embryo.

Question 35(b)

a) A doctor has advised Sameer to reduce sugar intake in his diet and do regular exercise after checking his blood test reports. Which disease do you think Sameer is suffering from? Name the hormone responsible for this disease and the organ producing the hormone.

b) Which hormone is present in the areas of rapid cell division in a plant and which hormone inhibits the growth?

Answer

a) Sameer is suffering from diabetes. In diabetes, there is rise in blood sugar level. The hormone responsible for this disease is insulin which is secreted from β-cells of pancreas.

b) Cytokinin is present in the areas of rapid cell division in a plant. Abscisic Acid inhibits the growth in plants.

Question 36(a)

The below image shows a thin lens of focal length 5 m.

(i) What is the kind of lens shown in the above figure?

(ii) If a real inverted image is to be formed by this lens at a distance of 7 m from the optical centre, then show with calculation where should the object be placed?

(iii) Draw a neatly labelled diagram of the image formation mentioned in (ii).

Answer

(i) Convex lens

(ii) Given,

Image distance (v) = 7 m

Focal length (f) = 5 m

Object distance (u) = ?

Using formula,

$\dfrac{1}{\text{f}}$ = $\dfrac{1}{\text{v}}$ - $\dfrac{1}{\text{u}}$

We get,

$\dfrac{1}{\text{5}}$ = $\dfrac{1}{\text{7}}$ - $\dfrac{1}{\text{u}}$

$\dfrac{1}{\text{u}}$ = $\dfrac{1}{\text{7}}$ - $\dfrac{1}{\text{5}}$ = $\dfrac{5-7}{\text{35}}$ = $\dfrac{-2}{\text{35}}$

So, u = - $\dfrac{35}{\text{2}}$ = -17.5 m

Hence, object should be placed at 17.5 m on the left side of the convex lens.

(iii) Below ray diagram shows the image formation:

Question 36(b)

A 10 cm long pencil is placed 5 cm in front of a concave mirror having a radius of curvature of 40 cm.

(i) Determine the position of the image formed by this mirror.

(ii) What is the size of the image?

(iii) Draw a ray diagram to show the formation of the image as mentioned in the part (i).

Answer

(i) Given,

Object distance (u) = -5 cm

Radius of curvature (r) = 40 cm

Image distance (v) = ?

Focal length (f) = $\dfrac{r}{2}$ = $\dfrac{40}{2}$ = -20 cm [f in case of a concave mirror is negative.]

Using formula,

$\dfrac{1}{\text{f}}$ = $\dfrac{1}{\text{v}}$ - $\dfrac{1}{\text{u}}$

We get,

-$\dfrac{1}{\text{20}}$ = $\dfrac{1}{\text{v}}$ - $\dfrac{1}{\text{5}}$

$\dfrac{1}{\text{v}}$ = -$\dfrac{1}{\text{20}}$ + $\dfrac{1}{\text{5}}$

$\dfrac{1}{\text{v}}$ = $\dfrac{-1+4}{\text{20}}$ = $\dfrac{3}{20}$

So, v = $\dfrac{20}{3}$ = 6.67 cm

Hence, image is obtained at 6.67 cm behind the mirror.

(ii) Size of object (h_o) = 10 cm

Size of the image (h_i)= ?

From formula,

m = $\dfrac{h_i}{h_o}$ = - $\dfrac{\text{v}}{\text{u}}$

Substituting we get,

$\dfrac{h_i}{10}$ = $-\dfrac{6.67}{-5}$

h_i = 10 x $\dfrac{6.67}{5}$ = 13.34 cm

Hence, size of image is 13.34 cm

(iii) Ray diagram showing the formation of the image is given below:

Section E (Source/Case Based Questions 4 Marks Each)

Question 37

The table given below shows the hints given by the quiz master in a quiz.

Based on the above hints answer the following questions

(a) Give the IUPAC names of A and F

(b) Illustrate with the help of chemical equations the changes taking place. (A ⟶ C and A ⟶ F)

OR

(b) Name the chemical reactions which occur in steps 2 and 5. Identify the compounds formed in these steps if 'A' is replaced with its next homologue.

Answer

(a) From step 3 we can conclude that A is Ethanol

From step 5 we can conclude that F is Ethene

$\underset{\text{ A} }{\text{CH}_3\text{CH}_2\text{OH}} \underset{ \text{H}_2\text{SO}_4}{\xrightarrow{\text{ Hot conc.}}} \underset{\text{ F}}{\text{CH}_2=\text{CH}_2 + {\text{H}_2\text{O}}}$

(b) A ⟶ C

$\underset{\text{ A} }{\text{CH}_3\text{CH}_2\text{OH}} \underset{ \text{ or acidified K}_2\text{Cr}_2\text{O}_7 + \text{{Heat}} }{\xrightarrow{\text{ alkaline KMNO}_4+ \text{Heat} + \text{ H}^+}} \underset{\text{ C} }{ \text{CH}_3\text{COOH} }$

A ⟶ F

$\underset{\text{ A} }{\text{CH}_3\text{CH}_2\text{OH}} \underset{ \text{H}_2\text{SO}_4}{\xrightarrow{\text{ Hot conc.}}} \underset{\text{ F}}{\text{CH}_2=\text{CH}_2 + {\text{H}_2\text{O}}}$

OR

(b) Step 2 is oxidation of ethanol.

$\underset{\text{ A} }{\text{CH}_3\text{CH}_2\text{OH}} \underset{ \text{ or acidified K}_2\text{Cr}_2\text{O}_7 + \text{{Heat}} }{\xrightarrow{\text{ alkaline KMNO}_4+ \text{Heat} + \text{ H}^+}} \underset{\text{ C} }{ \text{CH}_3\text{COOH} }$

Step 5 is hydrogenation as ethene reacts with hydrogen gas. It is also called an addition reaction.

CH₂ = CH₂ + H₂ ⟶ CH₃ - CH₃ [ethane]

When ethanol is replaced by propanol then propene is formed instead of ethene.

$\underset{\text{ Propanol} }{\text{C}_3\text{H}_7\text{OH}} \underset{ \text{H}_2\text{SO}_4}{\xrightarrow{\text{ Hot conc.}}} \underset{\text{ Propene}}{\text{C}_3\text{H}_6 + {\text{H}_2\text{O}}}$

Question 38

Figures (a) to (d) given below represent the type of ear lobes present in a family consisting of 2 children – Rahul, Nisha and their parents.

Excited by his observation of different types of ear lobes present in his family, Rahul conducted a survey of the type of ear lobes found {Figure (e) and (f)} in his classmates. He found two types of ear lobes in his classmates as per the frequency given below:

On the basis of above data answer the following questions.

(a) Which of the two characteristics - 'free ear lobe' or 'attached ear lobe' appears to be dominant in this case? Why?

(b) Is the inheritance of the free ear lobe linked with sex of the individual? Give reason for your answer.

(c) What type of ear lobe is present in father, mother, Rahul and his sister Nisha? Write the genetic constitution of each of these family members which explains the inheritance of this character in this family?

(Gene for Free ear lobe is represented by F and gene for attached ear lobe is represented by f for writing the genetic constitution).

OR

(c) Suresh's parents have attached ear lobes. What type of ear lobe can be seen in Suresh and his sister Siya? Explain by giving the genetic composition of all.

Answer

(a) Free ear lobe is dominant because it is found in a large majority of the population.

(b) No. It is not sex linked. As per the data of the family as well as the class, it is indicated that free ear lobe is present in males as well as in females.

(c)

• Father – Ff (free ear lobe)
• Mother – Ff (free ear lobe)
• Rahul – ff (attached ear lobe)
• Nisha – Ff or FF (free ear lobe)

Father and Mother are essentially heterozygous (Ff) for ear lobe. Nisha may be heterozygous (Ff) or homozygous (FF).

OR

(c) Suresh's father and mother are recessive homozygous (ff) as they have attached ear lobes. Since they do not have dominant gene for ear lobe, all their children will be recessive homozygous (ff) with attached ear lobes.

Question 39

Vinita and Ahmed demonstrated a circuit that operates the two headlights and the two sidelights of a car, in their school exhibition. Based on their demonstrated circuit, answer the following questions.

(i) State what happens when switch A is connected to

(a) Position 2

(b) Position 3

(ii) Find the potential difference across each lamp when lit.

(iii) Calculate the current

(a) in each 12 Ω lamp when lit.

(b) In each 4 Ω lamp when lit.

OR

(iv) Show, with calculations, which type of lamp, 4.0 Ω or 12 Ω, has the higher power.

Answer

(i) (a) When switch A is connected to position 2, circuit A-2 is complete and only 12 Ω lamps are on.

(b) When switch A is connected to position 3, circuit A-3 is complete and only 4 Ω lamps are on.

(ii) We know that when the resistances are connected in parallel, they have the same potential difference across their ends, hence, potential difference across each lamp when lit will be 12 V.

(iii) When the wire is connected to position 2, 12 Ω lamps are on.

Resistance of each lamp = 12 Ω

Voltage across each lamp = 12 V.

Using Ohm's Law: V = IR

Substituting we get,

12 = I x 12

I = $\dfrac{12}{12}$ = 1 A

Hence, current across each 12 Ω lamp is 1 A.

When the wire is connected to position 3, 4 Ω lamps are on.

Resistance of each lamp = 4 Ω

Voltage across each lamp = 12 V.

Using Ohm's Law: V = IR

Substituting we get,

12 = I x 4

I = $\dfrac{12}{4}$ = 3 A

Hence, current across each 4 Ω lamp is 3 A.

OR

(iv) Given,

All lamps are in parallel so V across each lamp = 12 V

We know, P = $\dfrac{V^2}{R}$

Substituting we get,

For 12 Ω lamps:

P = $\dfrac{12 \times 12}{12}$ = 12 W

For 4 Ω lamps:

P = $\dfrac{12 \times 12}{4}$ = 36 W

Hence, power across 4 Ω lamps will be higher.