Which one of the following is not an example of a redox reaction?

A redox reaction is defined by a change in the oxidation numbers of the elements involved. In option 1, the hydrolysis of aluminium trichloride (AlCl3 + 3H2O → Al(OH)3 + 3HCl) is a non-redox reaction [1]. In this process, aluminium remains in the +3 oxidation state, oxygen remains -2, and hydrogen remains +1; it is a double displacement/hydrolysis reaction where no electron transfer occurs. Conversely, option 2 involves the decomposition of sodium hydride where Na changes from +1 to 0 and H from -1 to 0. Option 3 is the oxidation of iron by oxygen to form iron(III) oxide, a classic redox process [2]. Option 4 is a single displacement reaction where zinc (0 to +2) displaces copper (+2 to 0), involving a clear change in oxidation states.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > Activity 3.9 > p. 41
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > CuO +H Cu+H O 2 2 → Heat (1.29) > p. 12