Explanation:

Except graying of hair, all the others are Physical changes as it involves changes in only size and shape. The graying of hair is a chemical change as it involves changes in constitution of hair.

Chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. These processes are called chemical reactions and, in general, are not reversible except by further chemical reactions.