When hydrogen peroxide is added to acidified potassium dichromate, a blue colour is produced due to formation of 

• A

  ${\mathrm{CrO}}_3$

• B

  ${\mathrm{Cr}}_2{\mathrm{O}}_3$

• C

  ${\mathrm{CrO}}_5$

• D

  ${\mathrm{CrO}}_4^{2-}$