Consider the following statements about the oxides of the 3d transition metals.
(A) V2O5 is amphoteric, though mainly acidic.
(B) The well characterised CrO is basic, but Cr2O3 is amphoteric.
(C) Ferrates(VI), (FeO4)2−, are formed in acidic media, but they readily decompose to Fe2O3 and O2.
(D) The ability of fluorine to stabilise high oxidation states exceeds that of oxygen.
(E) In the covalent oxide Mn2O7, each Mn is tetrahedrally surrounded by O atoms, including a Mn–O–Mn bridge.
Which of the statements given above are incorrect? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (C) and (D) only
The character of a metal oxide depends on the oxidation state of the metal: the lower oxides are basic and the higher oxides are amphoteric or acidic. Oxygen is very good at stabilising the highest oxidation states.
(A) V2O5 is amphoteric, though mainly acidic. — Correct statement. It gives VO43− salts (acidic behaviour) as well as VO2+ salts (basic behaviour).
(B) The well characterised CrO is basic, but Cr2O3 is amphoteric. — Correct statement. Chromium(II) oxide is the lower oxide, so it is basic; Cr(III) oxide is amphoteric.
(C) Ferrates(VI), (FeO4)2−, are formed in acidic media, but they readily decompose to Fe2O3 and O2. — Incorrect statement. Ferrates(VI) are formed in alkaline media, not acidic media. No oxide of iron higher than Fe2O3 is known.
(D) The ability of fluorine to stabilise high oxidation states exceeds that of oxygen. — Incorrect statement. It is the other way round: oxygen stabilises high states better. The highest fluoride of manganese is MnF4, but the highest oxide is Mn2O7, because oxygen can form multiple bonds to the metal.
(E) In the covalent oxide Mn2O7, each Mn is tetrahedrally surrounded by O atoms, including a Mn–O–Mn bridge. — Correct statement. In Mn2O7 manganese is in the +7 state, and the two MnO4 tetrahedra share one bridging oxygen.
NCERT (2026-27 edition):
4.3.7 Trends in Stability of Higher Oxidation States – “…Beyond Group 7, no higher oxides of Fe above Fe2O3, are known, although ferrates (VI)(FeO4)2–, are formed in alkaline media but they readily decompose to Fe2O3 and O2. … The ability of oxygen to stabilise these high oxidation states exceeds that of fluorine. Thus the highest Mn fluoride is MnF4 whereas the highest oxide is Mn2O7. The ability of oxygen to form multiple bonds to metals explains its superiority. In the covalent oxide Mn2O7, each Mn is tetrahedrally surrounded by O’s including a Mn–O–Mn bridge.”
4.4.1 Oxides and Oxoanions of Metals – “…V2O5 is, however, amphoteric though mainly acidic and it gives VO43– as well as VO2+ salts.” … “The well characterised CrO is basic but Cr2O3 is amphoteric.”