Which of the following statements is not correct?

• A
  $Mn_2O_7$ gives $HMnO_4$ on reaction with water.
• B
  On heating,$AgNO_3$ gives $Ag$,$NO_2$,and $O_2$.
• C
  $V_2O_5$ is amphoteric and dissolves in alkalies to give $VO_4^{3-}$ ions.
• D
  All of the above are incorrect.