Madhyamik Class 10 Physical Science Solved Paper 2025

(a) α-ray

Explanation

Alpha (α) rays have the highest ionising power because they possess a +2 charge and comparatively large mass.

(a) High resistance, low melting point

Explanation

A fuse wire is a safety device used to protect electrical circuits from damage caused by overloading or short circuits.

It should have:

• High resistance, so that it heats up quickly when excessive current flows.
• Low melting point, so that it melts easily and breaks the circuit before the appliances or wiring are damaged.

(d) 18

Explanation

The modern long form of the periodic table consists of 18 vertical columns, called groups, and 7 horizontal rows, called periods.

(d) NaCl

Explanation

Sodium chloride (NaCl) is an ionic compound. It does not exist as individual molecules; instead, it consists of a three-dimensional ionic crystal lattice made up of Na⁺ and Cl⁻ ions held together by strong electrostatic forces.

(a) CH₃COOH (Acetic acid)

Explanation

A weak electrolyte is a substance that partially ionises in aqueous solution, producing a relatively small number of ions. Therefore, it conducts electricity poorly.

(c) Green

Explanation

Hydrogen sulphide (H₂S) acts as a reducing agent. When it is passed through acidified potassium dichromate (K₂Cr₂O₇) solution, the orange-coloured dichromate ions (Cr₂O₇²⁻) are reduced to green-coloured chromium(III) ions (Cr³⁺).

(b) Bauxite

Explanation

Bauxite is the chief ore of aluminium. It mainly contains hydrated aluminium oxide (Al₂O₃·2H₂O) along with impurities such as iron oxide and silica.

(d) C₂H₂

Explanation

A triple bond unsaturated hydrocarbon is known as an alkyne. Alkynes contain at least one carbon-carbon triple bond (C≡C).

Among the given compounds:

• CH₄ (Methane) → Saturated hydrocarbon (single bonds only)
• C₂H₆ (Ethane) → Saturated hydrocarbon (single bonds only)
• C₂H₄ (Ethene) → Unsaturated hydrocarbon (double bond)
• C₂H₂ (Ethyne/Acetylene) → Unsaturated hydrocarbon (triple bond)

(c) Water vapour

Explanation

A greenhouse gas is a gas that absorbs and traps heat (infrared radiation) in the Earth’s atmosphere, causing the greenhouse effect and contributing to global warming.

(b) 11.2 litre

Explanation

Molar mass of CO₂ = 12 + (16 × 2) = 44 g/mol

Number of moles = \text{Mass} \over \text{Molar mass} = 22 \over 44  = 0.5 mol

Volume = Number of moles × 22.4 L

= 0.5 × 22.4

= 11.2 L

Therefore, the volume of 22 g of CO₂ at S.T.P. is 11.2 litres.

(b) 5.6 g

Explanation

Chemical Equation: CaCO₃ → CaO + CO₂

Masses →                    100            56

From the balanced equation,

100 g of CaCO₃ produces 56 g of CaO.

Therefore, Mass of CaO obtained from 10 g of CaCO₃

= \frac{56}{100}\times10

= 5.6 g

(b) Property of the material of the conductor

Explanation

The coefficient of thermal conductivity (k) is a property of the material that indicates how easily heat flows through it.

(c) Frequency

Explanation

When light travels from one transparent medium to another, its frequency remains unchanged because it is determined by the source of light.

(c) Convex mirror

Explanation

A convex mirror always forms an image that is:

• Virtual
• Erect
• Diminished (smaller than the object)

(c) Kilowatt-hour (kWh)

SI unit of radioactivity: Becquerel (Bq)

True

Explanation

Electrolysis is a chemical process in which an electric current brings about a chemical change in an electrolyte. During electrolysis, both oxidation and reduction occur simultaneously.

Acetic acid (CH₃COOH)

Hydrogen gas (H₂)

Iron (Fe)

Iron (Fe)

Explanation

The thermite process is used to extract or weld iron by reducing iron(III) oxide (Fe₂O₃) with aluminium powder. Aluminium, being more reactive than iron, removes oxygen from iron oxide to produce molten iron.

Chemical Equation: Fe₂O₃ + 2Al → Al₂O₃ + 2Fe

2-Bromopropane

Tetrafluoroethylene (TFE)

Chemical Formula: CF₂ = CF₂

Troposphere

Chlorofluorocarbon (CFC)

False

Explanation

At −273°C (0 K), the volume of an ideal gas is theoretically zero, not infinite.

3.01 × 10²³ molecules

Explanation

Molar mass of O₂ = 16 × 2 = 32 g/mol

Number of moles = \frac{\text{Mass}}{\text{Molar Mass}}

= \frac{16}{32}

= 0.5 mol

Number of molecules = 0.5 × 6.022 × 10²³ molecules

= 3.011 × 10²³ molecules ≈ 3.01 × 10²³ molecules

True

Explanation

The relationship between the coefficients of expansion for an isotropic solid is: γ = 3α

∴ γ = 3α = 3 × 1.2 × 10⁻⁵ = 3.6 × 10⁻⁵ /°C

Convex lens

Explanation

A convex lens is used as a magnifying glass because it forms a virtual, erect, and magnified image when the object is placed between the optical centre and the principal focus of the lens.

Angle of incidence = 0° (Normal incidence)

Miniature Circuit Breaker (MCB)

Voltage (V) = 220 V

Power (P) = 100 W

R = \frac{220^2}{100}

R = \frac{48400}{100} = 484 Ω

Formula of Fire Ice: CH₄·nH₂O (Methane Hydrate)

Methane gas is obtained by heating Fire Ice or by reducing the pressure.

Initial Volume (V₁) = 750 cc

Initial Temperature (T₁) = –3°C = 270 K

Final Volume (V₂) = 1000 cc

Final Temperature (T₂) = ?

From Charles Law: \text{V₁}\over \text{T₁} = \text{V₂}\over \text{T₂}

T₂ = \text{V₂ × T₁}\over \text{V₁} = \text{1000 × 270}\over \text{750} = 360 K

T₂ = 360 K – 273 K = 87 K

Hence, the final temperature of the gas is 87°C.

The ozone layer is called the natural sunscreen of the Earth because it absorbs most of the harmful ultraviolet (UV) rays coming from the Sun and protects living organisms.

Initial Pressure (P₁) = 76 cm Hg

Initial Volume (V₁) = 200 c.c.

Initial Temperature (T₁) = 27°C = 300 K

Final Pressure (P₂) = 38 cm Hg

Final Temperature (T₂) = 127°C = 400 K

Final Volume (V₂) = ?

From the Combined Gas Law, \frac{P_1V_1}{T_1}=\frac{P_2V_2}{T_2}

V₂ = \frac{P_1\times V_1\times T_2}{P_2\times T_1} = \frac{76\times200\times400}{38\times300} = 533.3 c.c.

Hence, the final volume of the gas is 533.3 c.c.

A concave lens always forms a virtual, erect and diminished image of an object. The image is formed between the optical centre (O) and the principal focus (F) on the same side of the lens as the object.

Resistance of the complete wire = 4 Ω

The wire is bent into a circle.

Therefore, the resistance of each semicircle = 4 ÷ 2 = 2 Ω

The two semicircles are connected in parallel between the ends of the diameter.

Equivalent resistance = \frac{R_1 \times R_2}{R_1 + R_2}

= \frac{2 \times 2}{2 + 2}

= \frac{4}{4}

= 1 Ω

Hence, the resistance across any diameter is 1 Ω.

Electron-dot structure of Calcium Oxide (CaO):

Electrovalent (Ionic) Compounds:

• LiH
• KCl

Covalent Compounds:

• NH₃
• C₂H₆

When dry ammonia gas is passed over heated sodium, sodamide (sodium amide) and hydrogen gas are formed.

Balanced Chemical Equation:

2Na + 2NH₃ → 2NaNH₂ + H₂↑

Modern Periodic Law

The physical and chemical properties of elements are periodic functions of their atomic numbers.

Periodic Trend of Atomic Radius

• Across a period (Group 1 → Group 2 and Group 13 → Group 17), the atomic radius decreases from left to right.
• This is because the nuclear charge increases, pulling the electrons closer to the nucleus while the number of electron shells remains the same.

During the electroplating of a brass spoon with nickel:

1. Cathode: Brass spoon
2. Anode: Pure nickel plate
3. Electrolyte: Aqueous solution of nickel sulphate (NiSO₄)

When hydrogen sulphide (H₂S) is passed through an aqueous solution of lead nitrate [Pb(NO₃)₂], a black precipitate of lead sulphide (PbS) is formed and nitric acid (HNO₃) is produced.

Balanced Chemical Equation:

Pb(NO₃)₂ + H₂S → PbS↓ + 2HNO₃

Observation:

A black precipitate of lead sulphide (PbS) is formed.

Use of CNG

• Compressed Natural Gas (CNG) is used as a clean fuel in automobiles because it produces less air pollution.

Harmful Effects

(i) Methanol: (a) Highly poisonous. (b) Consumption may cause blindness or even death.

(ii) Ethanol: (a) Excessive consumption affects the brain and liver. (b) It can lead to addiction and impaired judgment.

Avogadro’s Law : Equal volumes of all gases at the same temperature and pressure contain an equal number of molecules.

To show that moist air is lighter than dry air

According to Avogadro’s Law, equal volumes of gases contain an equal number of molecules.

Molecular mass of dry air ≈ 29

Molecular mass of H₂O = (2 × 1) + 16 = 18

When water vapour mixes with dry air, some of the heavier air molecules (average molecular mass = 29) are replaced by lighter water vapour molecules (molecular mass = 18).

Since 18 < 29, the average molecular mass of moist air decreases.

Therefore, moist air is lighter than dry air.

Mass of Mg = 1 g

Mass of O₂ = 0.5 g

Balanced Chemical Equation:

2Mg + O₂ → 2MgO

Molar mass of Mg = 24 g/mol

Molar mass of O₂ = 32 g/mol

From the balanced equation,

48 g of Mg reacts with 32 g of O₂.

Therefore, Mg required to react with 0.5 g of O₂

= \frac{48 \times 0.5}{32}

= 0.75 g

Available Mg = 1 g

Excess Mg = 1 − 0.75 = 0.25 g

Hence, magnesium remains in excess and the excess quantity is 0.25 g.

Gaps are left between railway rails to provide space for thermal expansion during hot weather. This prevents the rails from bending or buckling, thereby avoiding accidents.

The relation between the coefficients of expansion is:

α : β : γ= 1 : 2 : 3

At the first surface O, the ray enters the glass slab from air and is refracted.

According to Snell’s law, ₁μ₂ = sin i / sin r

where,

• i = angle of incidence,
• r = angle of refraction,
• ₁μ₂ = refractive index of glass with respect to air.

At the second surface B, the ray emerges from the glass into air.

Again, by Snell’s law, ₂μ₁ = sin r / sin θ (where θ is the angle of emergence)

Since, ₂μ₁ = 1 / ₁μ₂

⇒ sin i / sin r = sin θ / sin r

⇒ sin i = sin θ

⇒ θ = i

Thus, the angle of emergence is equal to the angle of incidence. Therefore, the emergent ray is parallel to the incident ray. However, it is displaced sideways by a small distance called the lateral shift.

Hypermetropia (Long-sightedness) is a defect of vision in which a person can see distant objects clearly but cannot see nearby objects distinctly.

It is corrected by using a convex lens.

Three resistors of 20 Ω each are connected in series.

Resistance in series = 20 + 20 + 20 = 60 Ω

This 60 Ω combination is connected in parallel with a 30 Ω resistor.

Equivalent resistance = \frac{R_1 \times R_2}{R_1 + R_2}

= \frac{60 \times 30}{60 + 30}

= \frac{1800}{90}

= 20 Ω

Hence, the equivalent resistance of the final combination is 20 Ω.

Let each resistor be R.

When connected in series,

Equivalent resistance = 3R

Given, Power dissipated = 10 W

Using the formula, P = \frac{V^2}{R}

⇒ 10 = \frac{V^2}{3R}

⇒ V² = 10 × 3R = 30 R

When the same resistors are connected in parallel,

Equivalent resistance = \frac{R}{3}

Power (P) = \frac{V^2}{R/3} = \frac{3V^2}{R}

Substituting V² = 30R,

P = \frac{3 \times 30R}{R} = 90 W

Hence, the power dissipated in the parallel combination is 90 W.

According to Lenz’s law, whenever there is a change in magnetic flux, the induced current always flows in a direction that opposes the change in magnetic flux.

For example, if a magnet is moved towards a coil, the induced current produces a magnetic field that opposes the approaching magnet. Therefore, an external force is required to keep the magnet moving.

If the induced current did not oppose the change, the magnet would continue to move on its own, producing electrical energy without any external work. This would violate the principle of conservation of energy.

Hence, Lenz’s law is consistent with the principle of conservation of energy.

Mass Defect : Mass defect is the difference between the sum of the masses of the individual nucleons (protons and neutrons) and the actual mass of the nucleus.

Given,

Mass of one proton = 1.00728 amu

Mass of one neutron = 1.00867 amu

Mass of helium nucleus = 4.0015 amu

A helium nucleus contains: 2 protons and 2 neutrons

Mass of 2 protons = 2 × 1.00728 = 2.01456 amu

Mass of 2 neutrons = 2 × 1.00867 = 2.01734 amu

Total mass of nucleons

= 2.01456 + 2.01734

= 4.03190 amu

Mass defect = Total mass of nucleons − Actual mass of nucleus

= 4.03190 − 4.00150

= 0.03040 amu

Hence, the mass defect of the helium nucleus is 0.0304 amu.

Ethene (Ethylene) – C₂H₄

Explanation

Ethene (ethylene) is a gaseous hydrocarbon that is used for the artificial ripening of fruits such as bananas, mangoes, and tomatoes. It acts as a plant hormone, accelerating the natural ripening process.

Ultraviolet (UV) rays can cause skin cancer.

The SI unit of resistivity (specific resistance) is ohm metre (Ω m).

At Standard Temperature and Pressure (S.T.P.), one mole of any gas occupies 22.4 litres.

Gamma (γ) rays

CH₃COOH (Acetic acid) is an organic compound because it contains carbon bonded directly to hydrogen (C–H bond), which is a characteristic feature of organic compounds.

Fleming’s left-hand rule states that when you stretch the thumb, forefinger, and middle finger of your left hand to be at right angles to each other, the forefinger points to the magnetic field, the middle finger points to the current, and the thumb shows the force.

Red colour is selected for danger signal lights because it has the longest wavelength and is scattered the least by the particles present in the atmosphere.

As a result, red light can travel a greater distance and remains clearly visible even in fog, mist, smoke, or dust. Therefore, it is used for danger signals, traffic lights, and stop signals.

Hydrogen sulphide (H₂S) reduces acidified potassium dichromate solution from orange to green.

Chemical Equation:

K₂Cr₂O₇ + 4H₂SO₄ + 3H₂S → Cr₂(SO₄)₃ + K₂SO₄ + 7H₂O + 3S