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

The phenomenon you're referring to is called sublimation. Sublimation is the process by which a solid substance directly turns into a gas, bypassing the liquid stage. This happens when the solid substance is exposed to air and the temperature is high enough to cause the particles in the solid to turn into a gas. For example, camphor and naphthalene are commonly used as air fresheners and moth repellents, and they tend to disappear over time because they sublime when exposed to air. Dry ice, which is the solid form of carbon dioxide, also sublimes at normal atmospheric pressure. So, in a nutshell, sublimation is the process of a solid turning directly into a gas without becoming a liquid first.