All the metals except scandium form MO oxides, which are ionic. Mn2O7 is a covalent green oil. In vanadium there is gradual change from the basic V2O3 to less basic V2O4 and to amphoteric V2O5 . V2O4 dissolves in acids to give VO2+ salts. Similarly, V2O5 reacts with alkalies as well as acids to give VO43− and VO4+ respectively. The well characterised CrO is basic but Cr2O3 is amphoteric.
(A) Mn2O7 is green oil at room temperature.
(B) V2O4 dissolve in acids to give VO2+ salts.
(C) CrO is basic oxide.
Hence option B is the answer,