A sample of any of the following substances disappears after sometime when exposed to air like camphor, naphthalene of dry ice. This phenomenon is called

The correct answer is A) Sublimation. Camphor, naphthalene balls and dry ice (solid CO₂) change directly from solid to vapour at ordinary temperature and pressure without passing through a liquid stage. That is why they seem to vanish from a open container over time.

• B) Evaporation is wrong. It is the change of a liquid into vapour at the surface. These substances do not need to melt first. Dry ice does not even form a liquid at 1 atm, so evaporation cannot describe it.
• C) Diffusion is wrong. It is the spreading of particles from higher to lower concentration, as when a perfume smell fills a room. It does not explain a solid itself disappearing.
• D) Radiation is wrong. It is the transfer of energy through electromagnetic waves or particles and has no bearing on change of state.

The core concept is change of state. Iodine and ammonium chloride are other standard examples of sublimation, and the process absorbs latent heat of sublimation. This links to the Class 9 matter chapter and to Mains questions on dry ice in cold-chain logistics.

Trap: Aspirants pick evaporation because the substance seems to disappear into the air. Evaporation needs a liquid stage, and that is missing here.