States of Matter and Gas Behaviour – NDA Chemistry PYQs

Q1. Which one of the following substances does not have a melting point?
(a) Ice (b) Sodium chloride (c) Mercury (d) Glass

Answer: (d) Glass
Glass is an amorphous solid with no regular crystal structure. It does not have a fixed melting point — it softens gradually over a range of temperatures. Ice, NaCl, and mercury are all crystalline or regular substances with definite melting points.
[NDA 2006-I]

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Q2. Glass is actually:
(a) A crystalline solid (b) An ionic solid (c) An elastic solid (d) A vitrified liquid

Answer: (d) A vitrified liquid
Glass is a supercooled liquid — a liquid that was cooled so slowly it became rigid without forming a crystal structure. It has no regular arrangement of atoms and no fixed melting point. It is vitrified (glass-like) rather than crystalline.
[NDA 2011-I]

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Q3. Glass is a:
(a) Liquid (b) Colloid (c) Non-crystalline amorphous solid (d) Crystalline solid

Answer: (c) Non-crystalline amorphous solid
Glass has no regular repeating atomic arrangement — it is amorphous (without form). It is often described as a supercooled liquid because it has the disordered structure of a liquid but the rigidity of a solid.
[NDA 2017-I]

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Q4. Which one of the following statements about glass is NOT correct?
(a) Glass is often said to be a supercooled liquid
(b) Glass has no definite melting point
(c) Soda glass is harder than Pyrex glass
(d) Boron is present in Pyrex glass

Answer: (c) Soda glass is harder than Pyrex glass
This is false. Pyrex (borosilicate glass) is harder and more resistant to heat and thermal shock than soda glass. Pyrex contains boron oxide which gives it superior properties. Soda glass is softer and cheaper — used for ordinary windows and bottles.
[NDA 2019-II]

Q5. Which one of the following is NOT used as a raw material in the manufacture of glass?
(a) Soda (b) Alumina (c) Borax (d) Gypsum

Answer: (d) Gypsum
Glass is made from silica (sand), soda ash (Na₂CO₃), and limestone (CaCO₃). Borax is used in borosilicate glass. Alumina is sometimes added. Gypsum (CaSO₄·2H₂O) is used in cement making — NOT in glass making.
[NDA 2021-I]

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Q6. Which one of the following is also known as Dry ice in its solid form?
(a) SiO₂ (b) CO₂ (c) CaO (d) MgO

Answer: (b) CO₂
Dry ice is solid carbon dioxide. It is called dry because it does not melt to a liquid at normal atmospheric pressure — it sublimes directly from solid to gas at −78°C. It is used as a refrigerant and for creating fog effects.
[NDA 2025-I]

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Q7. Which one of the following is termed as Dry ice?
(a) Ice present in ice-cream (b) Solid water at Antarctica (c) Solid state of carbon dioxide (d) Solid water of ionosphere

Answer: (c) Solid state of carbon dioxide
Dry ice = solid CO₂. It sublimes at −78°C, converting directly from solid to gas. It is used to keep items cold during transport without producing any liquid (hence “dry”).
[NDA 2019-II]

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Q8. 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
(c) Both boiling and evaporation are bulk phenomena
(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
Evaporation happens only at the surface of the liquid at any temperature. Boiling happens throughout the entire body of the liquid at the boiling point. This is the fundamental difference between the two processes.
[NDA 2019-II]

Q9. When does boiling of a liquid occur?
(a) When atmospheric pressure becomes equal to the vapour pressure
(b) When atmospheric pressure becomes less than vapour pressure
(c) When atmospheric pressure becomes higher than vapour pressure
(d) When vapour pressure becomes equal to the air pressure

Answer: (a) When atmospheric pressure becomes equal to the vapour pressure
A liquid boils when its vapour pressure rises to equal the atmospheric pressure. At sea level this happens at 100°C for water. At high altitude (lower atmospheric pressure), water boils below 100°C. In a pressure cooker (higher pressure inside), water boils above 100°C.
[NDA 2023-II]

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Q10. Which one of the following methods is used to separate anthracene from a mixture of anthracene and salt?
(a) Distillation (b) Sublimation (c) Evaporation (d) Chromatography

Answer: (b) Sublimation
Anthracene sublimes — it converts directly from solid to vapour on heating. Salt does not sublime. The vapour is cooled and anthracene is collected as a pure solid. Salt remains as residue.
[NDA 2021-II]

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Q11. Which one of the following is the best example of a desiccant?
(a) Silica gel (b) Polystyrene (c) Sodium chloride (d) Sodium carbonate

Answer: (a) Silica gel
Silica gel is the standard desiccant — it absorbs water vapour from its surroundings efficiently. It is found in small packets inside medicine bottles, electronics packaging, and shoe boxes. The others — polystyrene, NaCl, and Na₂CO₃ — do not function as desiccants.
[NDA 2020]

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Q12. A sulphur-containing compound is added to LPG cylinders because:
(a) It lowers the cost of production
(b) It enhances the efficiency of LPG
(c) It facilitates easy detection of leakage of the gas
(d) It assists in liquefying hydrocarbons

Answer: (c) It facilitates easy detection of leakage of the gas
Pure LPG (butane + propane) is colourless and completely odourless. Thioethanol (ethanethiol — a sulphur compound) is added to give it a strong, distinctive foul smell. If LPG leaks, you can smell it immediately before concentrations reach a dangerous level.
[NDA 2016-II]

Q13. Which one of the following is the major constituent of biogas?
(a) Carbon dioxide (b) Nitrous oxide (c) Methane (d) Oxygen

Answer: (c) Methane
Biogas is produced by anaerobic (without oxygen) decomposition of organic waste like cow dung. It contains approximately 55–65% methane as its primary combustible component. CO₂ makes up most of the remainder.
[NDA 2019-II]

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Q14. Which one of the following is considered to be the purest source of water?
(a) River water (b) Sea water (c) Well water (d) Rain water

Answer: (d) Rain water
Rain water is formed by natural evaporation and condensation — essentially a natural distillation process. It does not carry dissolved salts. River, sea, and well water all contain dissolved minerals and impurities.
[NDA 2025-II]

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Q15. Which one among the following does not wet the walls of the glass vessel in which it is kept?
(a) Water (b) Alcohol (c) Mercury (d) Kerosene

Answer: (c) Mercury
Mercury does not wet glass — its surface tension causes the meniscus to curve downward (convex meniscus). Most liquids (water, alcohol, kerosene) wet glass — their meniscus curves upward (concave meniscus). This difference is due to the cohesive forces within mercury being stronger than adhesive forces with glass.
[NDA 2015-I]

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Q16. Heating camphor is an example of which type of change?
(a) Chemical change (b) Physical change (c) Nuclear change (d) Electrochemical change

Answer: (b) Physical change
Camphor sublimes — it converts directly from solid to vapour. No new substance is formed. The chemical composition of camphor does not change. It is a physical change.
[NDA 2024-II]

Q17. Which of the following sets of substances can exist as molecular crystalline solids?
(a) Nickel, Zinc, Manganese
(b) Glass, Cement, Rubber
(c) Polyethene, Polyvinyl Chloride, Graphite
(d) Iodine, Sulphur, H₂O

Answer: (d) Iodine, Sulphur, H₂O
Molecular crystalline solids are made of molecules held together by weak intermolecular forces. Iodine (I₂), sulphur (S₈), and water (H₂O/ice) are all molecular solids. Metals (Ni, Zn, Mn) are metallic solids. Glass and rubber are amorphous. Graphite is a covalent network solid.
[NDA 2008-II]

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Q18. Refining of petroleum is carried out using which one of the following techniques?
(a) Evaporation (b) Fractional distillation (c) Separating funnel (d) Sublimation

Answer: (b) Fractional distillation
Crude oil contains many hydrocarbons with different boiling points. Fractional distillation separates them by heating the crude oil and collecting different fractions at different temperatures — LPG, petrol, kerosene, diesel, lubricating oil, and bitumen are collected at different levels.
[NDA 2022-I]

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Q19. Statement I: Glass is not considered as a true compound.
Statement II: Glass does not have a definite melting point.
(a) Both true, II correctly explains I
(b) Both true, II does not explain I
(c) I true, II false
(d) I false, II true

Answer: (b) Both true, II does not explain I
Both statements are true. Glass does not have a fixed composition (composition varies) — that is why it is not a true compound. Glass also has no definite melting point — it softens gradually. However, Statement II (no melting point) does not explain why glass is not a compound (Statement I is about composition, not melting point). Both facts are true but one does not explain the other.
[NDA 2013-II]