The oxide, in which metal is present in its intermediate oxidation state, is amphoteric in nature. The oxidation states of metal in the given oxides are as
+7
Mn
2O7,
+2
Cr2
O,
+4
V
2O4,
+3
Cr2
O3,
+3
V2
O3
Thus, Cr2O3 is an amphoteric oxide, i.e., it reacts with acids as well as base.