10th Science Important 2 Mark Questions with Answers

Secure your core foundational scores with our expert-compiled collection of 10th Science Important 2 Mark Questions. In the Class 10 Science exam, short-answer questions are the most effective way to accumulate marks quickly, testing your knowledge on direct scientific laws, core definitions, and straightforward formulas. This comprehensive repository brings together the most frequently repeated 2-mark questions across Physics, Chemistry, and Biology. Use this guide to sharpen your memory, recall essential terms instantly, and practice crisp, point-by-point presentation that evaluators love.

IMPORTANT TWO MARKS • PHYSICS & CHEMISTRY

PHYSICS

1. Laws of Motion

1. Define inertia. Give its classification.
The inability of the body to change its state is called inertia.
Types: (i) Inertia of rest (ii) Inertia of motion (iii) Inertia of direction

2. Classify the types of force based on their application.
Types of Forces: (i) Like parallel force (ii) Unlike parallel force

3. If a 5 N and a 15 N forces are acting opposite to one another. Find the resultant force and the direction of action of the resultant force.
F_net = F₂ − F₁ = 15 − 5 = 10 N.

4. Differentiate mass and weight.

Mass	Weight
1. It measures the quantity of matter.	1. It measures the gravitational force on a body.
2. SI unit is Kilogram (Kg).	2. SI unit is Newton (N).
3. Fundamental quantity.	3. Derived quantity.
4. Scalar quantity.	4. Vector quantity.

5. State Newton's second law.
Force ∝ rate of change of linear momentum of the body.

6. Why a spanner with a long handle is preferred to tighten screws in heavy vehicles?
The distance between line of action increases, the turning effect is also increased.

7. While catching a cricket ball the fielder lowers his hands backwards. Why?
To increase the time of contact, to reduce the impulse and the pain.

8. How does an astronaut float in a space shuttle?
Due to their huge orbital velocity.

Chap 2. Optics

1. What is refractive index?
Refractive index = Speed of light in vacuum / Speed of light in a medium • μ = c / v

2. State Snell's law (or) State Second law of refraction.
sin i / sin r = μ₂ / μ₁

3. Define dispersion of light.
Refraction of white light or composite light into its component colours.

4. State Rayleigh's law of scattering.
S ∝ 1 / λ⁴

5. Differentiate convex lens and concave lens.

Convex lens	Concave lens
1. Thicker in the middle.	1. Thinner in the middle.
2. Converging lens.	2. Diverging lens.
3. Produces real images mostly.	3. Produces only virtual images.
4. Used to treat Hypermetropia.	4. Used to treat Myopia.

6. What is power of accommodation of eye?
The ability of the eye lens to focus nearby as well as distant objects.

7. What are the causes of 'Myopia'?
Due to the lengthening of eye ball; the focal length of eye lens is reduced.

8. Why does the sky appear in blue colour?
By Rayleigh's law of scattering, blue colour of sunlight scatters the most by the atmosphere.

9. Why are traffic signals red in colour?
Red light has the longest wavelength and scatters less.

10. Write any two applications or uses of concave lens. [SEP - 2021]
• Used as eye lens of 'Galilean Telescope'
• Used to correct myopia

Chap 3. Thermal Physics

1. Define one calorie.
One calorie is the amount of heat energy required to rise the temperature of 1 gram of water through 1°C.

2. Distinguish between linear, areal or superficial expansion.

Linear Expansion	Areal / Superficial Expansion
1) When a body is heated or cooled, the length of the body changes.	1) When a body is heated or cooled, the area of the body changes.
2) Coefficient of linear expansion: α_L = ΔL / (L₀ ΔT)	2) Coefficient of Areal expansion: α_A = ΔA / (A₀ ΔT)

3. What is co-efficient of cubical expansion?
α_V = ΔV / (V₀ ΔT) • SI unit is K^-1.

4. State Boyle's law
P ∝ 1 / V ⇒ PV = constant.

5. State the law of volume
V ∝ T ⇒ V / T = constant.

6. Distinguish between ideal gas and real gas.

7. What is co-efficient of real expansion?
Coefficient of real expansion = Real rise in volume of the liquid per degree rise in temperature / unit volume.
Its SI unit is K^-1.

8. What is co-efficient of apparent expansion?
Coefficient of apparent expansion = Apparent rise in volume of the liquid per degree rise in temperature / unit volume.
Its SI unit is K^-1.

Chap 4. Electricity

1. What is the role of the earth wire in domestic circuits?
Earth wire acts as a protective conductor and saves us from electric shocks.

2. State Ohm's law.
I ∝ V ⇒ V = IR (where R → Resistance of the material).

3. What connection is used in domestic appliances and why?
Domestic appliances are connected in parallel.
Reason: Disconnection of one circuit does not affect other circuits; each appliance gets an equal voltage.

4. Distinguish between the resistivity and conductivity of a conductor.

Resistivity (ρ)	Conductivity (σ)
Resistance of a conductor of unit length and unit area of cross section.	Reciprocal of electrical resistivity.
Unit: ohm metre (Ω m).	Unit: ohm^-1 metre^-1 (Ω^-1 m^-1).
Measure of resisting power.	Ability to conduct electric current.

5. Define the unit of current.
SI unit of current is ampere (A). Current through a conductor is one ampere when a charge of one coulomb flows across its cross-section in one second.
1 ampere = 1 coulomb / 1 second

6. What happens to the resistance, as the conductor is made thicker?
Resistance decreases (because resistance is inversely proportional to the area of cross section).

7. Why is tungsten metal used in bulbs, but not in fuse wires?
Because of its high melting point, it is not used in fuse wires; but it is used in bulbs where it has to withstand high heat.

8. Name any two devices, which are working on the heating effect of the electric current.
Fuse wire, electric iron, toaster, oven, etc.

Chapter 5. Acoustics

1. Why does sound travel faster on a rainy day than on a dry day?
Presence of moisture in air decreases the density and increases the velocity of sound.

2. Why does an empty vessel produce more sound than a filled one?
Amplitude of vibration of air is greater than liquid.

3. Explain why, the ceilings of concert halls are curved.
Because sound intensity is maximized after multiple reflections and reaches every corner.

4. Mention two cases in which there is no Doppler effect in sound.
• When source (S) and listener (L) both are at rest.
• When source (S) and listener (L) move with constant distance between them.

5. Write any two applications of echo? [MAY-2022]
• Used by some animals to locate objects.
• Used in obstetric ultrasonography.

6. What is a longitudinal wave?
It is the wave in which particles vibrate along the direction of propagation of the wave.

7. What is the audible range of frequency? [SEP – 2021]
20 Hz to 20,000 Hz (or 20 kHz).

8. What is the minimum distance needed for an echo? [SEP – 2021, MDL-19]
17.2 m.

9. What will be the frequency of sound having 0.20 m as its wavelength, when it travels with a speed of 331 ms^-1?
n = v / λ = 331 / 0.20 = 3310 / 2 = 1655 Hz

10. Name three animals, which can hear ultrasonic vibrations.
1) Mosquito 2) Dogs 3) Bats

11. Difference between Sound and Light waves.

SOUND	LIGHT
Medium is required for propagation.	Medium is not required for propagation.
Longitudinal waves.	Transverse waves.
Speed = 340 ms^-1.	Speed = 3 × 10⁸ ms^-1.
Wavelength ranges from 1.65 cm to 1.65 m.	Wavelength ranges from 4 × 10^-7 m to 7 × 10^-7 m.

Chap 6. Nuclear Physics

One Mark Q/A:
1. Who discovered natural radioactivity? [MAY - 2022] → Henri Becquerel
2. Which radioactive material is present in pitchblende? → Radium, Uranium
3. Elements used for inducing radioactivity? → Boron, Aluminium
4. Radiation emitted during natural radioactivity: → Gamma
5. If element A emits an α-particle & produces ₁₀₄Rf²⁵⁹: → Mass number = 259 + 4 = 263 | Atomic number = 104 + 2 = 106
6. Average energy released from a single fission: → 3.2 × 10^-11 J (or 200 MeV)
7. Radiation causing genetic disease: → Gamma radiation
8. Radiation amount that causes death: → 600 R
9. First nuclear reactor built: → 1942 at Chicago, U.S.A
10. SI unit of radioactivity: → Becquerel (Bq)
11. Material that protects us from radiation: → Lead

1. Write any three features of natural and artificial radioactivity. [AUG-22, MAY-22, PTA-1]

Natural radioactivity	Artificial radioactivity
1. Spontaneous process.	1. Induced process.
2. Cannot be controlled.	2. Can be controlled.
3. Alpha, beta and gamma are emitted.	3. Elementary particles like neutron, positron, etc., are emitted.

2. Give the function of control rods in a nuclear reactor. [PTA - 3]
To control the number of neutrons. Ex: Boron, Cadmium rods.

3. In Japan, some newborn children are having congenital diseases. Why?
The atom bombs exploded in Japan emitted hazardous radiations causing genetic mutations and diseases.

4. Mr. Ramu is working as an X-ray technician but does not wear lead aprons. What suggestion will you give?
He should wear lead aprons to prevent exposure to hazardous radiation.

5. What is stellar energy?
The stars emit a large amount of energy in the form of light and heat via fusion. This energy is called stellar energy.

6. Give any two uses of radioisotopes in the field of agriculture.
Phosphorous isotopes (P-32):
• Increases the productivity of crops.
• Used to kill insects and parasites.

CHEMISTRY

7. Atoms and Molecules

1. Define: Relative Atomic Mass (or Standard atomic weight).
Relative Atomic Mass, A_r = Average mass of the isotopes of the element / (1/12^th mass of one carbon-12 atom).

2. Write the different types of isotopes of oxygen and its percentage abundance.

Isotope	Atomic Mass (amu)	% abundance
₈O¹⁶	15.9949	99.757
₈O¹⁷	16.9991	0.038
₈O¹⁸	17.9992	0.205

3. Define: Atomicity. Give an example. [AUG-2022, MAY-2022, SEP-2021]
Number of atoms present in a molecule is called its atomicity.
Ex: Atomicity of Phosphorous (P₄) is 4.

4. Give any two examples for hetero diatomic molecules. [AUG - 2022]
Hydrogen Chloride (HCl), Hydrogen Fluoride (HF).

5. What is Molar volume of a gas?
It is the volume occupied by one mole of a gas at STP. Its value is 22.4 litre / 22400 ml.

6. Find the percentage of nitrogen in ammonia. [PTA - 1]
% of Nitrogen in NH₃ = (Mass of element / Molecular mass) × 100 = (14 / 17) × 100 = 82.35%

4 Marks Problem: Calcium carbonate decomposition: CaCO₃ → CaO + CO₂
i) How many moles of Calcium carbonate are involved in this reaction? → One mole of CaCO₃
ii) Calculate the gram molecular mass of calcium carbonate: → (40 × 1) + (12 × 1) + (16 × 3) = 40 + 12 + 48 = 100 g
iii) How many moles of CO₂ are there in this equation? → One mole of CO₂

8. Periodic Classification of Elements

1. Metal A (reddish brown) combines with O₂:
• Below 1370 K: 2Cu + O₂ → 2CuO [B: Copper II oxide (black)]
• Above 1370 K: 4Cu + O₂ → 2Cu₂O [C: Copper I oxide (red)]
A → Copper (Cu) | B → Copper II oxide (CuO) | C → Copper I oxide (Cu₂O)

2. Metal A (silvery white) forms B at 800°C:
4Al + 3O₂ →_(800°C) 2Al₂O₃
A → Aluminium (Al) | B → Aluminium oxide (Al₂O₃)

3. What is rust? Give the chemical equation for formation of rust. [SEP – 2021, PTA-4]
When iron is exposed to moist air, it forms a layer of brown hydrated ferric oxide on its surface called rust.
4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O (Rust)

4. State two conditions necessary for rusting of iron:
Presence of air and water vapour.

9. Solutions

1. Define Solution:
A homogeneous mixture of two or more substances. Solute + Solvent = Solution. (Ex: Sea water).

2. What is meant by binary solution?
Binary solution consists of two components: one solute and one solvent (Ex: NaCl in water).

3. Give an example each:
i) Gas in liquid – Soda water
ii) Solid in liquid – NaCl in water
iii) Solid in solid – Copper in gold
iv) Gas in gas – Mixture of Helium and oxygen

4. What is aqueous and non-aqueous solution? Give an example.
• Aqueous solution: Water acts as a solvent (Ex: Sugar in water).
• Non-aqueous solution: Liquid other than water acts as solvent (Ex: Sulphur in CS₂).

5. Define Volume percentage:
Volume percentage = [Volume of solute / (Volume of solute + Volume of solvent)] × 100

6. Why do aquatic animals live more in cold regions?
Solubility of gas in liquid is higher at lower temperatures; thus, more oxygen dissolves in water.

7. Define Hydrated salt:
Ionic substances which contain water of crystallization (Ex: Blue vitriol CuSO₄·5H₂O).

8. A hot saturated solution of copper sulphate forms crystals as it cools. Why?
Solubility decreases with a decrease in temperature, causing excess copper sulphate to crystallize.

9. Classify substances into deliquescent and hygroscopic: [AUG - 2022]
• Deliquescent: Calcium chloride, Gypsum salt, Conc. Sulphuric acid
• Hygroscopic: Copper sulphate pentahydrate, Silica gel

10. Types of Chemical Reactions

1. Why does the reaction rate increase on raising the temperature?
Raising temperature provides more energy to break more bonds, increasing reaction rate.

2. Define combination reaction. Give one example:
A + B → AB (Element + Element → Compound) • Ex: C + O₂ → CO₂

3. Differentiate reversible and irreversible reactions:

Reversible reaction	Irreversible reaction
1. It can be reversed under suitable conditions.	1. It cannot be reversed.
2. Both forward and backward reactions occur.	2. Unidirectional (proceeds only in forward direction).
3. Attains equilibrium.	3. Equilibrium is not attained.
4. Relatively slow.	4. Fast.

11. Carbon and Its Compounds

1. Name the simplest ketone and give its structural or molecular formula:
• Simplest ketone: Acetone (Propanone)
• Structural formula: CH₃-CO-CH₃

2. How do detergents cause water pollution? Suggest remedial measures.
Some detergents have branched chains that are non-biodegradable by microorganisms, causing pollution.
Remedy: Use linear hydrocarbon chains which are easily biodegradable by bacteria.

3. Differentiate soaps and detergents.

Soaps	Detergents
1. Sodium salt of long chain fatty acids.	1. Sodium salts of sulphonic acids.
2. Ionic part is −COO⁻Na⁺.	2. Ionic part is −SO₃⁻Na⁺.
3. Ineffective in hard water.	3. Effective even in hard water.
4. Forms scum in hard water.	4. Does not form scum in hard water.
5. Poor foaming capacity.	5. Rich foaming capacity.
6. Biodegradable.	6. Mostly non-biodegradable.