Acidified potassium dichromate is treated with hydrogen sulphide. In the reaction the oxidation number of chromium?

Dichromate act as a strong oxidizing agent when it is treated with${\mathrm{H}}_2\mathrm{S}$, and then ${\mathrm{H}}_2\mathrm{S}$ will be oxidized into sulphur.

${\stackrel{+6}{\mathrm{Cr}}}_2{\mathrm{O}}_7^{-2}+3{\mathrm{H}}_2\stackrel{-2}{\mathrm{S}}+8{\mathrm{H}}^{+}\to 2{\mathrm{Cr}}^{+3}+3\stackrel{0}{\mathrm{S}}+ 7{\mathrm{H}}_2\mathrm{O}$

${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ act as an oxidizing agent.

Hence, the correct answer is option (B) decreases from +6 to +3.