JEE Main 2026 — d and f Block Elements Question with Solution

$K_{2}C{r}_2{O}_7$ in acidic medium acts as a strong oxidizing agent. It changes its colour from orange ($C{r}_2{O}_7^{2-}$) to green ($C{r}^{3+}$) when it reacts with a reducing agent.

We need to identify the set in which all species can act as reducing agents (i.e., they can be oxidized to a higher oxidation state).

In option (A), $F{e}^{2+}$ oxidizes to $F{e}^{3+}$, $S{n}^{2+}$ oxidizes to $S{n}^{4+}$, $I^{-}$ oxidizes to $I_2$, and $S^{2-}$ oxidizes to $S$. All of these are reducing agents.

In option (B), $F{e}^{3+}$ is already in its maximum stable oxidation state and cannot be oxidized further.

In option (C), $S{n}^{4+}$ cannot be oxidized further.

In option (D), $F{e}^{3+}$, $S{O}_4^{2-}$, and $S{n}^{4+}$ cannot be oxidized further.

Thus, only the species in option (A) will change the orange colour of $K_{2}C{r}_2{O}_7$.

Answer: $F{e}^{2+},S{n}^{2+},I^{-},S^{2-}$