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

1. A

   Sublimation

   (a) Sublimation. Camphor, naphthalene and dry ice pass from solid to vapour without a stable liquid, so the sample “disappears”. (a) Official key.

2. B

   Evaporation

   (b) Evaporation. That is liquid-to-vapour at the surface, not the solid camphor/naphthalene/CO2 path.

3. C

   Diffusion

   (c) Diffusion. Mixing of particles down a gradient; it does not name the phase change that empties the dish.

4. D

   Radiation

   (d) Radiation. Energy transfer by electromagnetic waves, not the vanishing of a solid sample in air.

Summary. Official key is (a). The vanishing of camphor, naphthalene or dry ice in air is sublimation. Evaporation needs a liquid; diffusion and radiation are other processes.