States of Matter and Gas Behaviour – NDA Chemistry PYQs

Solve NDA Chemistry previous-year questions on State of Matter with detailed solutions and explanations.

Chapter-wise PYQs • Concept-based explanations • Exam insights

NDA 2025-I

Q. 1. Which one of the following is also known as Dry ice in its solid form?

(a) SiO₂

(b) CO₂

(d) MgO

Answer: (b) CO₂

Explanation: Solid CO₂ (carbon dioxide) is known as dry ice. SiO₂ is silica/quartz. CaO is quicklime. MgO is magnesia. None of the others are called dry ice. Concept Tested: Dry ice = solid CO₂ – chemical identification

NDA 2024-II

Q. 2. The intermixing of particles of two different types of matter on their own is called

(a) Osmosis

(b) Brownian motion

(d) Conductance

Answer: (c) Diffusion

Explanation: Diffusion is the spontaneous intermixing of particles of two different substances due to their random motion, moving from a region of higher concentration to lower concentration. Osmosis specifically refers to solvent movement through a semi-permeable membrane. Brownian motion is the random movement of particles in a fluid. Concept Tested: Diffusion – definition and spontaneous intermixing

NDA 2022-II

Q. 3. Vapours of sulphur escaping from a volcano often form a crust on the rocks. The process involved is an example of

(a) condensation

(b) precipitation

(d) evaporation

Answer: (c) deposition

Explanation: Deposition is the direct conversion of a gas (or vapour) into a solid without passing through the liquid stage – the reverse of sublimation. Sulphur vapour solidifying on cold rocks is an example of deposition. Concept Tested: Deposition – gas to solid phase change

Q. 4. Dry ice is used on a performing stage to produce mist in air. The process involved is an example of

(a) sublimation

(b) evaporation

(d) precipitation

Answer: (a) sublimation

Explanation: Dry ice (solid CO₂) sublimes – converts directly from solid to gas. The cold CO₂ gas cools the surrounding air, causing water vapour in the air to condense and form a visible mist. The primary process of dry ice itself is sublimation. Concept Tested: Sublimation of dry ice – stage mist effect

NDA 2019-II

Q. 5. Which one of the following statements is correct?

(a) Both boiling and evaporation are surface phenomena.

(b) Boiling is a surface phenomenon, but evaporation is a bulk phenomenon.

(d) Boiling is a bulk phenomenon, but evaporation is a surface phenomenon.

Answer: (d) Boiling is a bulk phenomenon, but evaporation is a surface phenomenon.

Explanation: Evaporation occurs only at the surface of a liquid at any temperature. Boiling occurs throughout the bulk of the liquid when its vapour pressure equals atmospheric pressure at the boiling point. So evaporation is a surface phenomenon; boiling is a bulk phenomenon. Concept Tested: Difference between boiling and evaporation – surface vs bulk

★ JOVIK Exam Insight: NDA tests this distinction. Evaporation = surface only, any temperature. Boiling = entire liquid, at boiling point.

Q. 6. Which one of the following is termed as ‘Dry ice’?

(a) Ice present in ice-cream

(b) Solid water at Antarctica

(d) Solid water of ionosphere

Answer: (c) Solid state of carbon dioxide

Explanation: Dry ice is solid carbon dioxide (CO₂). It is called dry ice because it does not leave a wet residue on sublimation – it goes directly from solid to gas. Concept Tested: Dry ice – solid CO₂ (repeated question)

NDA 2018-II

Q. 7. Which one of the following is called dry ice?

(a) Solid carbon dioxide

(b) Liquid carbon dioxide

(d) Liquid ammonia

Answer: (a) Solid carbon dioxide

Explanation: Dry ice is solid CO₂. It is called “dry” because it sublimes directly to gas without forming liquid water. It is widely used as a refrigerant and in stage effects. Concept Tested: Dry ice – solid CO₂

NDA 2017-II

Q. 8. When pure water boils vigorously, the bubbles that rise to the surface are composed primarily of

(a) air

(b) hydrogen

(d) water vapour

Answer: (d) water vapour

Explanation: When pure water boils, the bubbles are composed of water vapour (steam). Boiling is the change of state from liquid to gas throughout the liquid. The bubbles are not air (water would need to be contaminated), not hydrogen or oxygen (water does not decompose merely by boiling). Concept Tested: Boiling of pure water – composition of bubbles

NDA 2016-I

Q. 9. When a solid is heated, it turns directly into a gas. This process is called

(a) Condensation

(b) Evaporation

(d) Diffusion

Answer: (c) Sublimation

Explanation: Sublimation is the direct conversion of a solid into vapour (gas) without passing through the liquid state. Examples: dry ice, camphor, naphthalene, iodine. Concept Tested: Sublimation – definition and examples

Q. 10. The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point. The melting point of a solid is an indication of

(a) strength of the intermolecular forces of attraction

(b) strength of the intermolecular forces of repulsion

(d) molecular size

Answer: (a) strength of the intermolecular forces of attraction

Explanation: A higher melting point means more energy is needed to break the intermolecular forces and change the solid to liquid. Therefore melting point is a direct measure of the strength of intermolecular attractive forces. Concept Tested: Melting point as indicator of intermolecular attractive forces

NDA 2015-I

Q. 11. Which one among the following does not wet the walls of the glass vessel in which it is kept ?

(a) Water

(b) Alcohol

(d) Phenol

Answer: (c) Mercury

Explanation: Mercury does not wet glass because its cohesive forces (mercury-mercury attraction) are stronger than the adhesive forces (mercury-glass attraction). This is why mercury forms a convex meniscus in glass. Water, alcohol and phenol all wet glass and form a concave meniscus. Concept Tested: Wetting and non-wetting of glass – cohesion vs adhesion

NDA 2014-I

Q. 12. The pressure of an ideal gas undergoing isothermal change is increased by 10%. The volume of the gas must decrease by about

(a) 0·1%

(b) 9%

(d) 0·9%

Answer: (b) 9%

Explanation: By Boyle’s Law: PV = constant at constant temperature. If P increases by 10%, new P = 1.1P. Then 1.1P × V_new = P × V → V_new = V/1.1 ≈ 0.909V. Decrease = (1 − 1/1.1) = 1/11 ≈ 9.09% ≈ 9%. Concept Tested: Boyle’s Law – pressure-volume relationship for isothermal change

NDA 2009-II

Q. 13. Dry ice is used for making cold-baths in laboratories by mixing with volatile organic solvents. Identify the form of dry ice from the following

(a) Gaseous carbon dioxide

(b) Liquid carbon dioxide

(d) Solid hydrogen oxide

Answer: (c) Solid carbon dioxide

Explanation: Dry ice is the solid form of carbon dioxide (CO₂). It sublimes directly from solid to gas at −78.5 °C without passing through a liquid stage at normal atmospheric pressure. This sublimation absorbs heat, making it effective for cold baths. Concept Tested: Dry ice – solid CO₂ and sublimation

★ JOVIK Exam Insight: Dry ice = solid CO₂. NDA has asked this identification multiple times across different papers. Never confuse with liquid N₂ or liquid CO₂.