Crystallization of sodium chloride This is a physical change. The sodium chloride (table salt) is changing its form from a dissolved state in water to a solid crystal structure, but the chemical composition remains NaCl.

Melting of ice Similar to crystallization, melting of ice is a physical change. Water (H2O) molecules are rearranging from a rigid solid structure to a more fluid liquid state, but the chemical makeup stays the same.

Souring of milk This is a chemical change. Milk sugar (lactose) is broken down by bacteria into lactic acid. This process involves the formation of new substances and alters the chemical composition of the milk.

Therefore, only statement 3 is an example of chemical change.