Question

Acidified potassium dichromate is treated with hydrogen sulphide. In the reactiion, the oxidation number of chromium
A. Increases from `+ 3` to `+ 6`
B. decreases from `+ 6` to `+ 3`
C. Remains unchanged
D. Decreases from `+ 6` to `+ 2`

Answer 1

Correct Answer - B
Decrease from `+ 6 ` to `+ 3`.
`K_(2) Cr_(2) O_(7) + 4H_(2) SO_(4) rarr K_(2) SO_(4) + Cr_(2) (SO_(4))_(3) + 4 H_(2) O + 3O`
`[H_(2) S + [O] rarr S + H_(2) O] xx 3`
`bar(K_(2) overset(+6)Cr2O_(7) + 4H_(2) SO_(4) + 3 H_(2) S rarr K_(2) SO_(4) + overset(+3)Cr (SO_(4))_(3) + 7 H_(2) O + 3S)`