Which phenomenon is opposite to solidification?

The correct option is Fusion.

Explanation:
Phase transitions describe the transformation of matter from one state (solid, liquid, or gas) to another.

1. Solidification: Also known as freezing, solidification is the process in which a substance changes from the liquid phase to the solid phase when heat energy is removed.

2. Fusion: Also commonly known as melting, fusion is the process in which a substance changes from the solid phase to the liquid phase upon absorbing heat energy.

Because solidification converts a liquid into a solid while fusion converts a solid into a liquid, fusion is the phenomenon opposite to solidification.

Overview of Other Options:
• Vaporisation: The process of changing from a liquid state to a gaseous state.
• Sublimation: The direct transition of a substance from the solid state to the gas state without passing through the liquid phase.
• Condensation: The process of changing from a gaseous state to a liquid state (the opposite of vaporisation).