Which change involves a solid turning directly into a gas without becoming a liquid?

• A. Deposition
• B. Melting
• C. Sublimation
• D. Freezing

Answer: (C)

Sublimation is the process where a solid turns directly into a gas without becoming a liquid. This happens when the molecules at the solid’s surface gain enough energy to overcome the lattice forces and escape into the air as gas, rather than melting into a liquid first. In other words, the solid’s vapor pressure is sufficient to push molecules into the gas phase at that temperature and pressure.

Think of dry ice (solid CO2) or certain crystals like iodine as classic examples that sublimate at room temperature. Deposition is the opposite (gas turning into solid), melting is solid to liquid, and freezing is liquid to solid, so they don’t describe a solid going straight to gas.