Phase change when heat is added to a solid?

• A. Melting (solid → liquid)
• B. Freezing
• C. Condensation
• D. Sublimation

Answer: (A)

When heat is added to a solid, its particles gain energy until they can overcome the forces holding the structure together, allowing the material to flow as a liquid. At the melting point, the solid begins to melt, and the added energy goes into breaking those bonds rather than raising temperature, so the temperature stays nearly constant during the transition. This is known as melting (solid to liquid). After melting, further heating can raise the temperature of the liquid. The other options describe different changes: freezing is liquid to solid; condensation is gas to liquid; sublimation is solid to gas without becoming liquid under certain conditions.