JEE Main 2026 — Chemistry Physical Chemistry

2026mcqmedium

Consider the following reduction processes :

$\mathrm{Al}^{3+}+3 \mathrm{e}^{-} \longrightarrow \mathrm{Al}(\mathrm{s}), \mathrm{E}^{0}=-1.66 \mathrm{~V}$

$\mathrm{Fe}^{3+}+\mathrm{e}^{-} \longrightarrow \mathrm{Fe}^{2+}, \mathrm{E}^{0}=+0.77 \mathrm{~V}$

$\mathrm{Co}^{3+}+\mathrm{e}^{-} \longrightarrow \mathrm{Co}^{2+}, \mathrm{E}^{0}=+1.81 \mathrm{~V}$

$\mathrm{Cr}^{3+}+3 \mathrm{e}^{-} \longrightarrow \mathrm{Cr}(\mathrm{s}), \mathrm{E}^{\circ}=-0.74 \mathrm{~V}$

The tendency to act as reducing agent decreases in the order :

Official previous-year question

Held on 22 Jan 2026 · Verified 6 Jul 2026.

Options

A
$\mathrm{Al}>\mathrm{Cr}>\mathrm{Fe}^{2+}>\mathrm{Co}^{2+}$
B
$\mathrm{Cr}>\mathrm{Fe}^{2+}>\mathrm{Al}>\mathrm{Co}^{2+}$
C
$\mathrm{Al}>\mathrm{Fe}^{2+}>\mathrm{Cr}>\mathrm{Co}^{2+}$
D
$\mathrm{Al}>\mathrm{Cr}>\mathrm{Co}^{2+}>\mathrm{Fe}^{2+}$

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Solution

Reducing agent strength is determined by oxidation potential (opposite sign of reduction potential). Stronger reducing agents have more negative oxidation potentials (easier to oxidize).

Oxidation potentials:

Al(s) → Al³⁺ has E° = +1.66 V (strongest reducing agent);

Cr(s) → Cr³⁺ has E° = +0.74 V;

Fe²⁺ → Fe³⁺ has E° = -0.77 V;

Co²⁺ → Co³⁺ has E° = -1.81 V (weakest reducing agent).

Order of decreasing reducing agent tendency: Al > Cr > Fe²⁺ > Co²⁺.

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Options

$\mathrm{Al}>\mathrm{Cr}>\mathrm{Fe}^{2+}>\mathrm{Co}^{2+}$

$\mathrm{Cr}>\mathrm{Fe}^{2+}>\mathrm{Al}>\mathrm{Co}^{2+}$

$\mathrm{Al}>\mathrm{Fe}^{2+}>\mathrm{Cr}>\mathrm{Co}^{2+}$

$\mathrm{Al}>\mathrm{Cr}>\mathrm{Co}^{2+}>\mathrm{Fe}^{2+}$

Solution

Reducing agent strength is determined by oxidation potential (opposite sign of reduction potential). Stronger reducing agents have more negative oxidation potentials (easier to oxidize).

Oxidation potentials:

Al(s) → Al³⁺ has E° = +1.66 V (strongest reducing agent);

Cr(s) → Cr³⁺ has E° = +0.74 V;

Fe²⁺ → Fe³⁺ has E° = -0.77 V;

Co²⁺ → Co³⁺ has E° = -1.81 V (weakest reducing agent).

Order of decreasing reducing agent tendency: Al > Cr > Fe²⁺ > Co²⁺.

JEE Main 2026 — Chemistry Physical Chemistry

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JEE Main 2026 — Chemistry Physical Chemistry

Options

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Solution

Your note

JEE Main Physical Chemistry in other years

More JEE Main Physical Chemistry questions

Other Chemistry topics for JEE Main

Organic Chemistry

Inorganic Chemistry

Keep practicing Physical Chemistry