JEE Main 2021 — Chemistry Inorganic Chemistry

2021integermedium

The total number of unpaired electrons present in $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{2}$ and $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{3}$ is

Official previous-year question

Held on 22 Jul 2021 · Verified 6 Jul 2026.

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Solution

$[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]{\mathrm{Cl}}_{2}$

${\mathrm{Co}}^{2+}:[\mathrm{Ar}]3{d}^{7}4{s}^{0}4{p}^{0}$

For strong field ligand and ${d}^{7}$ configuration: ${t}_{2g}^{2,2,2}{e}_{g}^{1,0}$

Total $1$ unpaired electron is present.

$[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]{\mathrm{Cl}}_{3}$

${\mathrm{Co}}^{3+}:[\mathrm{Ar}]3{d}^{6}4{s}^{0}4{p}^{0}$

The hybridisation of the complex is ${d}^{2}{\mathrm{sp}}^{3}$ hybridisation.

${\mathrm{NH}}_{3}$ acts as strong field ligand, because ${\Delta }_{0}>P.E.$ .

So here all electrons becomes paired.

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JEE Main 2021 — Chemistry Inorganic Chemistry

2021integermedium

Official previous-year question

Held on 22 Jul 2021 · Verified 6 Jul 2026.

Did you get this right?

Solution

$[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]{\mathrm{Cl}}_{2}$

${\mathrm{Co}}^{2+}:[\mathrm{Ar}]3{d}^{7}4{s}^{0}4{p}^{0}$

For strong field ligand and ${d}^{7}$ configuration: ${t}_{2g}^{2,2,2}{e}_{g}^{1,0}$

Total $1$ unpaired electron is present.

$[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]{\mathrm{Cl}}_{3}$

${\mathrm{Co}}^{3+}:[\mathrm{Ar}]3{d}^{6}4{s}^{0}4{p}^{0}$

The hybridisation of the complex is ${d}^{2}{\mathrm{sp}}^{3}$ hybridisation.

${\mathrm{NH}}_{3}$ acts as strong field ligand, because ${\Delta }_{0}>P.E.$ .

So here all electrons becomes paired.

Your note

JEE Main Inorganic Chemistry in other years

Keep practicing Inorganic Chemistry

Work through every JEE Main Inorganic Chemistry PYQ, year by year.

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JEE Main 2021 — Chemistry Inorganic Chemistry

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Solution

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JEE Main Inorganic Chemistry in other years

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JEE Main 2021 — Chemistry Inorganic Chemistry

Did you get this right?

Solution

Your note

JEE Main Inorganic Chemistry in other years

More JEE Main Inorganic Chemistry questions

Other Chemistry topics for JEE Main

Physical Chemistry

Organic Chemistry

Keep practicing Inorganic Chemistry