The process whereby a substance changes from a solid to liquid when heat is applied, is called?

Step 1: Analyze the question The question asks for the name of the process where a solid turns into a liquid when heat is applied.

Step 2: Explain the concept When a solid is heated, its particles gain kinetic energy and vibrate faster. At a certain temperature (the melting point), the forces holding the particles in fixed positions are overcome, and the solid becomes a liquid. In physics, this change of state is called melting, or fusion. The heat absorbed during the change is the latent heat of fusion.

Step 3: Check each option

• A. Evaporation: liquid changes to vapour at the surface, at any temperature below boiling. This is not the answer.
• B. Vaporization: liquid changes to gas, either by boiling or by evaporation. This is not the answer.
• C. Fission: the splitting of a heavy nucleus into lighter nuclei. This is a nuclear process, not a change of state.
• D. Fusion: solid changes to liquid. This matches the question. (The word "fusion" is also used in nuclear physics for the joining of light nuclei, but in the context of heat and states of matter it means melting.)

Step 4: Answer The correct option is D. Fusion.

Step 5: Exam tip Remember the state changes in order:

• Solid → Liquid: Fusion (melting)
• Liquid → Gas: Vaporization
• Gas → Liquid: Condensation
• Liquid → Solid: Solidification (freezing)

Link "fusion" with "fuse" (to melt together), and "latent heat of fusion" with melting ice. You can do this!