Question:
Dichromate ion is treated with base, the oxidation number of $\mathrm{Cr}$ in the product formed is:
Solution:
(6)
$\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+2 \mathrm{OH}^{-}=2 \mathrm{CrO}_{4}^{2-}+\mathrm{H}_{2} \mathrm{O}$
$2 \mathrm{CrO}_{7}^{2-}$
$\mathrm{x}+(-2 \times 4)=-2$
$x=6$