Explanation

(c)
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ K_{2}Cr_{2}O_{7} + \ H_{2}SO_{4}\ \rightarrow K_{2}SO_{4} + \ H_{2}Cr_{2}O_{7}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 4\left\lbrack H_{2}O_{2}\ \rightarrow H_{2}O + O \right\rbrack$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ H_{2}Cr_{2}O_{7} + \ 4O\ \rightarrow 2CrO_{5} + \ H_{2}O$
$K_{2}Cr_{2}O_{7} + \ H_{2}SO_{4} + \ 4H_{2}O_{2}\ \rightarrow 2CrO_{5} + \ K_{2}SO_{4} + \ 5\ H_{2}O$
Acidified $K_{2}Cr_{2}O_{7}$ is oxidised to blue peroxide of chromium $\left( CrO_{5} \right)$ which is soluble in ether and produces blue coloured solution.