Which of the statements given below is incorrect? 

• A

  ${\mathrm{O}}_3$ molecule is bent.

• B

  ${\mathrm{O}}_2{ \mathrm{N}}^{-}$ and  ONF is isoelectronic 

• C

  ${\mathrm{OF}}_2$ is an oxide of fluorine.

• D

  ${\mathrm{Cl}}_2{\mathrm{O}}_7$ is anhydride of perchloric acid