Final answer:
Sublimation can occur because like liquids, solids have a vapor pressure, which allows them to change directly from a solid to a gas under certain conditions.
Step-by-step explanation:
Sublimation can occur because solids, like liquids, have a vapor pressure. The correct option in the final answer is (d) Vapor Pressure. When a solid has sufficient vapor pressure and the conditions such as temperature and external pressure allow, it can transform directly from a solid state to a gaseous state without first becoming a liquid. This process is illustrated by the phase diagram where the solid-vapor curve indicates the temperatures and pressures at which a substance can sublimate.
For example, dry ice (solid CO₂) sublimes at atmospheric pressure without melting, demonstrating its vapor pressure in action.