Which one of the following is a chemical change ?

A chemical change involves the formation of one or more new substances through a chemical reaction [1]. Graying of hair naturally is a chemical change because it involves the reduction or absence of melanin pigments (eumelanin and phaeomelanin) due to biochemical processes in the body. This process alters the chemical composition of the hair shaft, resulting in a new color state that cannot be reversed by physical means. In contrast, cutting hair or fruit are physical changes because they only alter the size or shape without changing the chemical structure of the keratin or fruit tissue [2]. Swelling of resin in water is typically a physical change involving the absorption of water molecules into the polymer matrix without forming a new chemical substance. Therefore, the natural graying of hair is the only option representing a fundamental chemical transformation.

Sources

1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 5: Changes Around Us: Physical and Chemical > In a Nutshell > p. 68
2. [2] Science-Class VII . NCERT(Revised ed 2025) > Chapter 5: Changes Around Us: Physical and Chemical > Fig. 5.2: Blowing air in (a) tap water; (b) lime water > p. 60