MHTCET 17 Apr 2026 Shift 1 Paper

Concept:A redox reaction involves a change in the oxidation numbers of the reacting species.Explanation:Consider option D: $\mathrm{HCl}+\mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{H}_{3}\mathrm{O}^{+}+\mathrm{Cl}^{-}$.In this reaction, hydrogen remains at $+1$, oxygen remains at $-2$, and chlorine remains at $-1$.Since there is no change in oxidation numbers, neither oxidation nor reduction takes place.This is simply an acid-base reaction in which $\mathrm{HCl}$ donates a proton to water.Hence, option D is not a redox reaction.In option A, sulphur changes from $+4$ to $+6$, while chlorine changes from $0$ to $-1$.In option B, zinc changes from $0$ to $+2$, while copper changes from $+2$ to $0$.In option C, hydrogen changes from $0$ to $+1$, while oxygen changes from $0$ to $-2$.Thus, options A, B, and C show clear oxidation number changes.Answer:The reaction that is NOT a redox reaction is option D: $\mathrm{HCl}+\mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{H}_{3}\mathrm{O}^{+}+\mathrm{Cl}^{-}$.