Which one of the following is not a chemical change ?

A physical change involves a change in physical properties like shape, size, or state without forming a new substance [5]. Freezing of water is a physical change because it only involves a change of state from liquid to solid, which can be reversed by melting [5]. In contrast, a chemical change results in the formation of one or more new substances through chemical reactions [4]. Ripening of fruits involves enzymatic and biochemical changes that alter the fruit's composition [3]. Curdling of milk is a chemical process where proteins undergo coagulation and denaturation to form a new substance, curd [6]. Digestion of food is a complex chemical change where enzymes break down food into different chemical components to sustain life [2]. Therefore, freezing of water is the only option that is not a chemical change.

Sources

1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 5: Changes Around Us: Physical and Chemical > In a Nutshell > p. 68
2. [5] Science-Class VII . NCERT(Revised ed 2025) > Chapter 5: Changes Around Us: Physical and Chemical > C. Crushing a piece of chalk > p. 59
3. [4] 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
4. [3] Science-Class VII . NCERT(Revised ed 2025) > Chapter 5: Changes Around Us: Physical and Chemical > 5.6 Are All Changes Desirable? > p. 66
5. [2] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > p. 1
6. [6] https://pmc.ncbi.nlm.nih.gov/articles/PMC8410156/