Which one among the following is a chemical process?

A chemical process involves the formation of new substances through chemical reactions, whereas physical processes only change the state or appearance of matter [2]. Distillation of seawater (Option 1) and crystallization of salt (Option 2) are physical separation techniques based on boiling points and solubility, respectively, where no new chemical species are created [t4][t8]. Sublimation of iodine (Option 4) is a phase transition from solid to gas, which is a physical change [t9]. In contrast, the production of iodine from seaweeds (Option 3) is a chemical process. Seaweeds contain iodine in the form of iodide ions (I⁻) [t1]. Extracting elemental iodine (I2) requires a chemical reaction, typically involving the oxidation of these iodide ions using an oxidizing agent or through the combustion of seaweed to ash followed by chemical treatment [t7]. Because a new substance (I2) is formed from ionic precursors, it is classified as a chemical process.

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