An aqueous solution of X on addition of hydrogen peroxide in ice...

Both chromate and dichromate radicals on reaction with acidified $\mathrm{H}_{2} \mathrm{O}_{2}$ give blue solution which turns green on standing. In the presence of organic solvents such as diethyl ether, amyl alcohol or pyridine, permanent blue colour obtained.
$\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{4}+\mathrm{H}_{2} \mathrm{SO}_{4}+\mathrm{H}_{2} \mathrm{O}_{2} \stackrel{\text { Ether }}{\longrightarrow} \mathrm{CrO}_{5}+\mathrm{K}_{2} \mathrm{SO}_{4} +\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}+4 \mathrm{H}_{2} \mathrm{SO}_{4}+4 \mathrm{H}_{2} \mathrm{O}_{2} \stackrel{\text { Ether }}{\longrightarrow} \underset{\text { (Blue colour) }}{2 \mathrm{CrO}_{5}}+\mathrm{K}_{2} \mathrm{SO}_{4} +5 \mathrm{H}_{2} \mathrm{O}$