Why does camphor disappear if kept in the open air for a few days?

Camphor disappears when kept in open air for a few days due to a process called sublimation. Sublimation is the transition of a substance from the solid phase directly to the gaseous phase, bypassing the liquid phase. Camphor is a volatile compound that readily undergoes sublimation at room temperature.

When camphor is exposed to the open air, the molecules on the surface of the solid camphor gain enough energy from the surroundings to break the intermolecular forces holding them together. As a result, these molecules transition directly into the gas phase without first becoming a liquid. This process occurs continuously, and over time, the camphor gradually sublimate and disappears.

Therefore, 'It undergoes sublimation from solid to gas directly.' is the correct answer.