Which of the following sets includes all the species that will change the orange colour of $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$ in acidic medium?

(A) $\mathrm{Fe}^{2+}, \mathrm{Sn}^{2+}, \mathrm{I}^{-}, \mathrm{S}^{2-}$

(B) $\mathrm{S}^{2-}, \mathrm{Fe}^{3+}, \mathrm{I}^{-}, \mathrm{C}_{2} \mathrm{O}_{4}^{2-}$

(C) $\mathrm{Fe}^{2+}, \mathrm{NO}_{2}^{-}, \mathrm{SO}_{2}, \mathrm{Sn}^{4+}$

(D) $\mathrm{Fe}^{3+}, \mathrm{SO}_{4}^{2-}, \mathrm{S}^{2-}, \mathrm{Sn}^{4+}$

JEE Main · 2026 · 02 Apr 2026 · Shift 1 · d and f Block Elements

Which of the following sets includes all the species that will change the orange colour of

K_{2} Cr_{2} O_{7}

in acidic medium?

Answer: (A)

Dichromate is orange and turns green as it is reduced to

C r^{3 +}

, so the colour changes only when every species present is a reducing agent. In the chosen set

F e^{2 +} \to F e^{3 +}

S n^{2 +} \to S n^{4 +}

I^{-} \to I_{2}

and

S^{2 -} \to S

are all oxidisable, so all four reduce dichromate. The remaining sets contain already-oxidised species such as

F e^{3 +}

S n^{4 +}

S O_{4}^{2 -}

that cannot reduce it, so only the first set qualifies.

JEE Main · 2026 · 02 Apr 2026 · Shift 1 · Single correct option