JEE Mains Chemistry · The d- and f-Block Elements

Oxides of Transition Metals

A transition metal's oxides turn from basic to amphoteric to acidic as its oxidation state rises, and the highest oxides such as Mn₂O₇ are covalent molecules built from shared tetrahedra.

All The d- and f-Block Elements notes JEE Mains Chemistry strategy

Why this matters

Eighteen PYQs, fourteen of them multiple choice, and two from 2026. Twelve ask whether an oxide is basic, amphoteric or acidic, most often for vanadium and chromium, and several then ask for the magnetic moment of the metal in it; six are about the structure of Mn₂O₇ and the mixed oxides such as Fe₃O₄. One rule, oxidation state against acidity, answers most of the page.

Concept 1 of 2: Basic, amphoteric and acidic oxides

In a low oxidation state the metal ion is large and weakly polarising, so its oxide is ionic and basic, like an s-block oxide. As the oxidation state rises the metal pulls the oxide electrons towards itself, the bonding turns covalent, and the oxide starts to behave like a non-metal oxide: acidic. The middle states are amphoteric.

Definition

Rule: for one metal, higher oxidation state → less ionic, less basic, more acidic.
Vanadium: $\mathrm{V_2O_3}$ (+3) basic > $\mathrm{V_2O_4}$ (+4) less basic > $\mathrm{V_2O_5}$ (+5) amphoteric, mainly acidic.
$\mathrm{V_2O_4}$ dissolves in acids to give vanadyl salts, $\mathrm{VO^{2+}}$ .
$\mathrm{V_2O_5}$ gives $\mathrm{VO_4^{3-}}$ in alkali and $\mathrm{VO_2^{+}}$ in acid. V stays +5 in both.
Chromium: CrO basic, $\mathrm{Cr_2O_3}$ amphoteric, $\mathrm{CrO_3}$ acidic (gives $\mathrm{H_2CrO_4}$ and $\mathrm{H_2Cr_2O_7}$ ).
Manganese: MnO basic, $\mathrm{Mn_2O_7}$ acidic (gives $\mathrm{HMnO_4}$ ).
Zinc: ZnO and $\mathrm{Zn(OH)_2}$ are amphoteric. $\mathrm{Zn + 2NaOH + 2H_2O \rightarrow Na_2[Zn(OH)_4] + H_2}$ .
Cr³⁺ with dilute NaOH: a green precipitate of hydrated $\mathrm{Cr_2O_3}$ ( $\mathrm{Cr_2O_3 \cdot nH_2O}$ ); in excess alkali it dissolves as $\mathrm{[Cr(OH)_4]^{-}}$ .

Oxide	Metal oxidation state	Character	With acid or alkali
$\mathrm{V_2O_3}$	+3	Basic	Dissolves in acid to give $\mathrm{V^{3+}}$ salts
$\mathrm{V_2O_4}$	+4	Less basic (weakly amphoteric)	Dissolves in acid to give $\mathrm{VO^{2+}}$ salts
$\mathrm{V_2O_5}$	+5	Amphoteric, mainly acidic	$\mathrm{VO_4^{3-}}$ in alkali, $\mathrm{VO_2^{+}}$ in acid The contact-process catalyst, but not a basic oxide.
CrO	+2	Basic	Dissolves in acid to give $\mathrm{Cr^{2+}}$
$\mathrm{Cr_2O_3}$	+3	Amphoteric	Reacts with both acid and alkali
$\mathrm{CrO_3}$	+6	Acidic	With water gives chromic acid, $\mathrm{H_2CrO_4}$
MnO	+2	Basic	Dissolves in acid to give $\mathrm{Mn^{2+}}$
$\mathrm{Mn_2O_7}$	+7	Acidic	With water gives permanganic acid, $\mathrm{HMnO_4}$
ZnO	+2	Amphoteric	Zincate, $\mathrm{[Zn(OH)_4]^{2-}}$ , in excess alkali

Down each metal's column of oxides, the character moves from basic to acidic as the oxidation state rises.

Practice this conceptself-check · 5 quick reps

The same idea in a real exam question:

JEE Mains · 2023 · 31 January 2023 · Q47Moderate

Example 1 · The d- and f-Block Elements · Oxides of Transition Metals

The correct order of basicity of oxides of vanadium is

V₂O₄ with acid gives VO²⁺

Vanadium(IV) in acid is the vanadyl ion,

\mathrm{VO^{2+}}

. The ion

\mathrm{VO_2^{+}}

is vanadium(V), formed from

\mathrm{V_2O_5}

. Match the oxidation state before choosing.

Ionic character falls as the oxidation state rises

A higher oxidation state gives a MORE covalent oxide, which is why

\mathrm{Mn_2O_7}

is a liquid and not an ionic solid. A statement that ionic character increases with oxidation number is false.

Drill 11 more on basic, amphoteric and acidic oxides

Concept 2 of 2: Structure of Mn₂O₇ and the mixed oxides

The highest oxides are not ionic lattices.

\mathrm{Mn_2O_7}

is a molecule: two

\mathrm{MnO_4}

tetrahedra joined through one shared oxygen. Oxygen holds manganese at +7 because each terminal oxygen forms a double bond. A mixed oxide is different again: one formula that hides two oxidation states of the same metal.

Definition

Mn₂O₇: each Mn is tetrahedral. Two tetrahedra share one corner oxygen.
7 oxygens: 1 bridging (two Mn–O–Mn bonds) and 6 terminal (six Mn=O bonds). There is no Mn–Mn bond.
It is covalent: a green oil at room temperature.
Mixed oxides hold one metal in two states: $\mathrm{Mn_3O_4}$ (MnO· $\mathrm{Mn_2O_3}$ ), $\mathrm{Fe_3O_4}$ (FeO· $\mathrm{Fe_2O_3}$ ), $\mathrm{Co_3O_4}$ (CoO· $\mathrm{Co_2O_3}$ ). Each has +2 and +3.
Average oxidation state in $\mathrm{M_3O_4}$ is $+8/3$ , which is the sign of a mixed oxide.
$\mathrm{Fe_2O_3}$ , $\mathrm{Cr_2O_3}$ , $\mathrm{V_2O_4}$ and $\mathrm{Ti_2O_3}$ hold one state only: not mixed.
Oxidation state in the common oxides: $\mathrm{Fe_2O_3}$ +3 < $\mathrm{MnO_2}$ +4 < $\mathrm{V_2O_5}$ +5 < $\mathrm{CrO_3}$ +6.

Oxide	Metal oxidation state	Structure or make-up	Point tested
$\mathrm{Mn_2O_7}$	+7	Two $\mathrm{MnO_4}$ tetrahedra sharing one O	6 terminal Mn=O, 1 bridging O, covalent green oil Mn is tetrahedral, not octahedral, and there is no Mn–Mn bond.
$\mathrm{CrO_3}$	+6	Chains of $\mathrm{CrO_4}$ tetrahedra sharing corners	Acidic, strong oxidant
$\mathrm{Mn_3O_4}$	+2 and +3	MnO· $\mathrm{Mn_2O_3}$	Mixed oxide; paramagnetic
$\mathrm{Fe_3O_4}$	+2 and +3	FeO· $\mathrm{Fe_2O_3}$	Mixed oxide; magnetite, strongly magnetic
$\mathrm{Co_3O_4}$	+2 and +3	CoO· $\mathrm{Co_2O_3}$	Mixed oxide
$\mathrm{Fe_2O_3}$	+3	One oxidation state	Not a mixed oxide

A formula M₃O₄ with an average state of +8/3 hides a +2 and a +3 metal.

Practice this conceptself-check · 5 quick reps

The same idea in a real exam question:

JEE Mains · 2026 · 21 Jan 2026 Shift 2 · Q41Moderate

Example 2 · The d- and f-Block Elements · Oxides of Transition Metals

Given below are some of the statements about Mn and

Mn_{2}O_{7}

. Identify the correct statements (A) Mn forms the oxide

{Mn}_{2}O_{7}

in which Mn is in its highest oxidation state. (B) Oxygen stabilizes the Mn in higher oxidation states by forming multiple bonds with Mn (C)

{Mn}_{2}O_{7}

is an ionic oxide. (D) The structure of

{Mn}_{2}O_{7}

consists of one bridged oxygen. Choose the correct answer from the options given below:

Mn₂O₇ is covalent, not ionic

It is a molecular liquid. A statement calling

\mathrm{Mn_2O_7}

an ionic oxide is false; so is one that puts Mn in an octahedron.

An M₂O₃ or M₃O₄ formula alone does not decide 'mixed'

Check for two oxidation states.

\mathrm{Fe_3O_4}

is mixed (+2 and +3);

\mathrm{Fe_2O_3}

is all +3 and

\mathrm{V_2O_4}

all +4.

Drill 5 more on structure of mn₂o₇ and the mixed oxides

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Reference tables (2)

Basic, amphoteric and acidic oxides9 rows

Oxide	Metal oxidation state	Character	With acid or alkali
$\mathrm{V_2O_3}$	+3	Basic	Dissolves in acid to give $\mathrm{V^{3+}}$ salts
$\mathrm{V_2O_4}$	+4	Less basic (weakly amphoteric)	Dissolves in acid to give $\mathrm{VO^{2+}}$ salts
$\mathrm{V_2O_5}$	+5	Amphoteric, mainly acidic	$\mathrm{VO_4^{3-}}$ in alkali, $\mathrm{VO_2^{+}}$ in acid The contact-process catalyst, but not a basic oxide.
CrO	+2	Basic	Dissolves in acid to give $\mathrm{Cr^{2+}}$
$\mathrm{Cr_2O_3}$	+3	Amphoteric	Reacts with both acid and alkali
$\mathrm{CrO_3}$	+6	Acidic	With water gives chromic acid, $\mathrm{H_2CrO_4}$
MnO	+2	Basic	Dissolves in acid to give $\mathrm{Mn^{2+}}$
$\mathrm{Mn_2O_7}$	+7	Acidic	With water gives permanganic acid, $\mathrm{HMnO_4}$
ZnO	+2	Amphoteric	Zincate, $\mathrm{[Zn(OH)_4]^{2-}}$ , in excess alkali

Down each metal's column of oxides, the character moves from basic to acidic as the oxidation state rises.

Structure of Mn₂O₇ and the mixed oxides6 rows

Oxide	Metal oxidation state	Structure or make-up	Point tested
$\mathrm{Mn_2O_7}$	+7	Two $\mathrm{MnO_4}$ tetrahedra sharing one O	6 terminal Mn=O, 1 bridging O, covalent green oil Mn is tetrahedral, not octahedral, and there is no Mn–Mn bond.
$\mathrm{CrO_3}$	+6	Chains of $\mathrm{CrO_4}$ tetrahedra sharing corners	Acidic, strong oxidant
$\mathrm{Mn_3O_4}$	+2 and +3	MnO· $\mathrm{Mn_2O_3}$	Mixed oxide; paramagnetic
$\mathrm{Fe_3O_4}$	+2 and +3	FeO· $\mathrm{Fe_2O_3}$	Mixed oxide; magnetite, strongly magnetic
$\mathrm{Co_3O_4}$	+2 and +3	CoO· $\mathrm{Co_2O_3}$	Mixed oxide
$\mathrm{Fe_2O_3}$	+3	One oxidation state	Not a mixed oxide

A formula M₃O₄ with an average state of +8/3 hides a +2 and a +3 metal.

Watch out for (4)

V₂O₄ with acid gives VO²⁺
→ Basic, amphoteric and acidic oxides
Ionic character falls as the oxidation state rises
→ Basic, amphoteric and acidic oxides
Mn₂O₇ is covalent, not ionic
→ Structure of Mn₂O₇ and the mixed oxides
An M₂O₃ or M₃O₄ formula alone does not decide 'mixed'
→ Structure of Mn₂O₇ and the mixed oxides

Test yourself on The d- and f-Block Elements

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Related notes

Oxidation States and Electrode Potentials — which states each metal shows →