MHTCET 13 Apr 2026 Shift 1 Paper

Concept:A redox reaction involves simultaneous oxidation and reduction, meaning oxidation numbers of some elements change.If no element changes its oxidation number, the reaction is not a redox reaction.Explanation:Check the oxidation numbers in each option.Option A: $\mathrm{Zn}$ changes from $0$ to $+2$, and $\mathrm{H}$ changes from $+1$ to $0$.Both oxidation and reduction occur, so it is a redox reaction.Option B: In $\mathrm{Al(OH)_3}$ and $\mathrm{AlCl_3}$, $\mathrm{Al}$ remains $+3$.Hydrogen remains $+1$ in both $\mathrm{HCl}$ and $\mathrm{H_2O}$.Chlorine remains $-1$, and oxygen remains $-2$ throughout.No oxidation number changes, so it is only an acid-base neutralisation reaction.Option C: $\mathrm{Mg}$ changes from $0$ to $+2$, and $\mathrm{O}$ changes from $0$ to $-2$.Option D: $\mathrm{Fe}$ changes from $0$ to $+2$, and $\mathrm{Cu^{2+}}$ changes from $+2$ to $0$.Thus, only Option B shows no change in oxidation numbers.Answer:Option B: $\mathrm{Al(OH)_3 + 3HCl \rightarrow AlCl_3 + 3H_2O}$ is NOT a redox reaction.