The sum of the total number of sigma bonds between chromium and oxygen atoms in chromate and dichromate ions is

Solution

In chromate $\mathrm{C}\mathrm{r}{\mathrm{O}}_4^{2-}$ and dichromate $\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_7^{2-}$ there are 4 and 8 $\mathrm{C}\mathrm{r}-\mathrm{O}$ bonds are there as follows



Total number of Cr-O bond = 12.

Hence, the correct answer is 12.