Change of physical state of a substance from solid state to liquid state is known as:

Fusion

The correct answer is option 3. Fusion.

Change of physical state of a substance from solid state to liquid state is known as Fusion.

Fusion, also known as melting, is the process by which a substance changes from its solid state to its liquid state. During fusion, the substance absorbs heat energy, causing its particles to gain enough kinetic energy to overcome the attractive forces holding them in a fixed position in the solid lattice. As a result, the particles break free from their fixed positions and begin to move more freely, forming a liquid.