Solution:Concept- When the physical state of substance changes like from solid to liquid, liquid to gas, this is known as phase change processes.
Melting is a physical process that causes a solid to liquid phase shift.For example- ice melts to form water.
Freezing is a physical process in which a liquid changes into solid form. For example- water freezes and converts to ice.
Liquefaction is the transformation of a gas into a liquid state. It is also known as condensation. For example- conversion of water vapours into liquid water.
Thus, the correct option is 2) Freezing.