JEE Main 2023 — Chemistry Inorganic Chemistry

2023mcqmedium

Which of the following complex is octahedral, diamagnetic and the most stable?

Official previous-year question

Held on 8 Apr 2023 · Verified 6 Jul 2026.

Options

A
${\mathrm{Na}}_{3}[{\mathrm{CoCl}}_{6}]$
B
$[\mathrm{Ni}{({\mathrm{NH}}_{3})}_{6}]{\mathrm{Cl}}_{2}$
C
${K}_{3}[\mathrm{Co}(\mathrm{CN}{)}_{6}]$
D
$[\mathrm{Co}{({H}_{2}O)}_{6}]{\mathrm{Cl}}_{2}$

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Solution

The coordination compound ${K}_{3}[\mathrm{Co}(\mathrm{CN}{)}_{6}]$ contains a cobalt( $\mathrm{III}$ ) ion, which has a ${d}^{6}$ electronic configuration. The cyanide ligands in this complex are indeed strong field ligands, which means they will cause a large splitting of the $d$ orbitals. So here cobalt is in $+3$ state having $3{d}^{6}$ configuration and also cyanide ligand which is a strong field ligand so, it is most stable and will have octahedral shape. The given compounds have the following nature:

(1) ${\mathrm{Na}}_{3}[{\mathrm{CoCl}}_{6}]$ – Paramagnetic

(2) $[\mathrm{Ni}{({\mathrm{NH}}_{3})}_{6}]{\mathrm{Cl}}_{2}$ – Paramagnetic

(3) ${K}_{3}[\mathrm{Co}(\mathrm{CN}{)}_{6}]$ – Diamagnetic

(4) $[\mathrm{Co}{({H}_{2}O)}_{6}]{\mathrm{Cl}}_{2}$ – Paramagnetic

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Options

${\mathrm{Na}}_{3}[{\mathrm{CoCl}}_{6}]$

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

${K}_{3}[\mathrm{Co}(\mathrm{CN}{)}_{6}]$

$[\mathrm{Co}{({H}_{2}O)}_{6}]{\mathrm{Cl}}_{2}$

Solution

(1) ${\mathrm{Na}}_{3}[{\mathrm{CoCl}}_{6}]$ – Paramagnetic

(2) $[\mathrm{Ni}{({\mathrm{NH}}_{3})}_{6}]{\mathrm{Cl}}_{2}$ – Paramagnetic

(3) ${K}_{3}[\mathrm{Co}(\mathrm{CN}{)}_{6}]$ – Diamagnetic

(4) $[\mathrm{Co}{({H}_{2}O)}_{6}]{\mathrm{Cl}}_{2}$ – Paramagnetic

JEE Main 2023 — Chemistry Inorganic Chemistry

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JEE Main 2023 — Chemistry Inorganic Chemistry

Options

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Solution

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JEE Main Inorganic Chemistry in other years

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Other Chemistry topics for JEE Main

Physical Chemistry

Organic Chemistry

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