On heating a mixture of common salt and $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$ in equal amount along with concentrated $\mathrm{H}_{2} \mathrm{SO}_{4}$ in a test tube, a gas is evolved. Formula of the gas evolved and oxidation state of the central metal atom in the gas respectively are:

(B) $\mathrm{CrO}_{2} \mathrm{Cl}_{2}$ and +6

(A) $\mathrm{CrO}_{2} \mathrm{Cl}_{2}$ and +5

(C) $\mathrm{Cr}_{2} \mathrm{O}_{2} \mathrm{Cl}_{2}$ and +6

(D) $\mathrm{Cr}_{2} \mathrm{O}_{2} \mathrm{Cl}_{2}$ and +3

JEE Main · 2026 · 21 Jan 2026 · Shift 2 · d and f Block Elements

On heating a mixture of common salt and

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

in equal amount along with concentrated

H_{2} SO_{4}

in a test tube, a gas is evolved. Formula of the gas evolved and oxidation state of the central metal atom in the gas respectively are:

Answer: (B)

Heating sodium chloride with potassium dichromate in concentrated sulphuric acid evolves the deep red vapour of chromyl chloride,

4 NaCl + K_{2} Cr_{2} O_{7} + 6 H_{2} SO_{4} \to 2 CrO_{2} Cl_{2} + 2 KHSO_{4} + 4 NaHSO_{4} + 3 H_{2} O

. In

CrO_{2} Cl_{2}

the two oxygens account for

- 4

and the two chlorines for

- 2

, so chromium must be

+ 6

to leave the molecule neutral. The gas evolved is chromyl chloride,

CrO_{2} Cl_{2}

, with chromium in the +6 oxidation state.

JEE Main · 2026 · 21 Jan 2026 · Shift 2 · Single correct option