Which of the following are amphoteric oxides?
$Mn_2O_7, CrO_3, Cr_2O_3, CrO, V_2O_5, V_2O_4$

Which of the following metals becomes passive when treated with concentrated $HNO_3$?

Which of the following metal oxides is not amphoteric?

How would you account for the increasing oxidising power in the series $VO_2^+ < Cr_2O_7^{2-} < MnO_4^-$?

Given below are two statements:
Assertion $(A)$: All $Cu$ $(II)$ halides are known except the iodide.
Reason $(R)$: $Cu^{2+}$ oxidizes $I^{-}$ to $I_2$.
The correct answer is:

Select the incorrect statement.