The conversion of ${\mathrm{CrO}}_4^{2-}$ to ${\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}$in the acidic medium is an example of

In acidic medium , yellow chromate ion is converted into orange red dichromate ion, it is a condensation reaction

 $2{\mathrm{CrO}}_4^{2-}+2{\mathrm{H}}^{+}\rightleftharpoons {\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}+{\mathrm{H}}_2\mathrm{O}$