NEET UG 2011 — Chemistry Inorganic Chemistry

2011mcqmedium

Which of the following complex compounds will exhibit highest paramagnetic behaviour? (At. no. : $\mathrm{Ti}=22, \mathrm{Cr}=24$ , $\mathrm{Co}=27, \mathrm{Zn}=30$ )

Official previous-year question

Held on 30 Apr 2011 · Verified 9 Jul 2026.

Options

A
$\left[\mathrm{Ti}\left(\mathrm{NH}_3\right)_6\right]^{3+}$
B
$\left[\mathrm{Cr}\left(\mathrm{NH}_3\right)_6\right]^{3+}$
C
$\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}$
D
$\left[\mathrm{Zn}\left(\mathrm{NH}_3\right)_6\right]^{2+}$

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Solution

(A) Electronic configuration of $\mathrm{Ti}^{3+}$ in $\left[\mathrm{Ti}\left(\mathrm{NH}_3\right)_6\right]^{3+}$ NEET 2011 Chemistry, Coordination Compounds — solution figure 1

(B) Electronic configuration of $\mathrm{Cr}^{3+}$ in $\left[\mathrm{Cr}\left(\mathrm{NH}_3\right)_6\right]^{3+}$ NEET 2011 Chemistry, Coordination Compounds — solution figure 2

(C) Electronic configuration of $\mathrm{Co}^{3+}$ in $\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}$ : NEET 2011 Chemistry, Coordination Compounds — solution figure 3

In the presence of strong field ligand $\mathrm{NH}_3$ , pairing of electrons takes place and thus, octahedral complex, $\quad\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}$ is diamagnetic. $\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}$ $\left[\begin{array}{l} \text { inner orbital or } \\ \text { low spin complex } \end{array}\right]\left(6 \mathrm{NH}_3 \text { molecules }\right)$ NEET 2011 Chemistry, Coordination Compounds — solution figure 4

(D) Electronic configuration of $\mathrm{Zn}^{2+}$ in $\left[\mathrm{Zn}\left(\mathrm{NH}_3\right)_6\right]^{2+}$ : NEET 2011 Chemistry, Coordination Compounds — solution figure 5

$\therefore\left[\mathrm{Zn}\left(\mathrm{NH}_3\right)_6\right]^{2+}$ is an outer orbital complex and is diamagnetic.

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Options

$\left[\mathrm{Ti}\left(\mathrm{NH}_3\right)_6\right]^{3+}$

$\left[\mathrm{Cr}\left(\mathrm{NH}_3\right)_6\right]^{3+}$

$\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}$

$\left[\mathrm{Zn}\left(\mathrm{NH}_3\right)_6\right]^{2+}$

Solution

(A) Electronic configuration of $\mathrm{Ti}^{3+}$ in $\left[\mathrm{Ti}\left(\mathrm{NH}_3\right)_6\right]^{3+}$ NEET 2011 Chemistry, Coordination Compounds — solution figure 1

(B) Electronic configuration of $\mathrm{Cr}^{3+}$ in $\left[\mathrm{Cr}\left(\mathrm{NH}_3\right)_6\right]^{3+}$ NEET 2011 Chemistry, Coordination Compounds — solution figure 2

(C) Electronic configuration of $\mathrm{Co}^{3+}$ in $\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}$ : NEET 2011 Chemistry, Coordination Compounds — solution figure 3

(D) Electronic configuration of $\mathrm{Zn}^{2+}$ in $\left[\mathrm{Zn}\left(\mathrm{NH}_3\right)_6\right]^{2+}$ : NEET 2011 Chemistry, Coordination Compounds — solution figure 5

$\therefore\left[\mathrm{Zn}\left(\mathrm{NH}_3\right)_6\right]^{2+}$ is an outer orbital complex and is diamagnetic.

NEET UG 2011 — Chemistry Inorganic Chemistry

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NEET UG 2011 — Chemistry Inorganic Chemistry

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