The d electron configuration of Cr^ 2+ , Mn^ 2+ , Fe^ 2+ and Ni^ 2+ are 3 ~d^4, 3 ~d^5, 3 ~d^6 and 3 ~d^8 respectively. Which one of the following aqua complexes will exhibit the minimum paramagnetic behaviour? (At. No.

Correct answer: B. [Ni (H_2 O)_6]^ 2+ aligned & Cr^ ++ (3 d^4)= array |l|l|l|l|l| 1 & 1 & 1 & 1 & array & =4 unpaired e^ - & Mn^ ++ (3 d^4)= array |l|l|l|l|l| 1 & 1 & 1 & 1 & 1 array & =5 unpaired e^ - & Fe^ ++ (3 d^6)= 1L 1 1 1 1 & =4 unpaired e^ - & Ni^ ++ (3 d^8)= 1h 1L IL 1 1 & =2 unpaired e^ - & aligned As Ni^ ++ has minimum no. of unpaired e^ - thus this is least paramagnetic.

NEET 2007

Exam: NEET
Year: 2007
Subject: Chemistry
Chapter: Coordination Compounds

NEET 2007 · Chemistry · Coordination Compounds

The d electron configuration of Cr^ 2+ , Mn^ 2+ , Fe^ 2+ and Ni^ 2+...

The

d

electron configuration of

\mathrm{Cr}^{2+}

\mathrm{Mn}^{2+}, \mathrm{Fe}^{2+}

and

\mathrm{Ni}^{2+}

are

3 \mathrm{~d}^4, 3 \mathrm{~d}^5, 3 \mathrm{~d}^6

and

3 \mathrm{~d}^8

respectively. Which one of the following aqua complexes will exhibit the minimum paramagnetic behaviour? (At. No.

\mathrm{Cr}=24, \mathrm{Mn}=25, \mathrm{Fe}=26, \mathrm{Ni}=

28)

Options

A\left[\mathrm{Fe} $\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$
B\left[\mathrm{Ni} $\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$
C\left[\mathrm{Cr} $\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$
D\left[\mathrm{Mn} $\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$

Correct answer

B. \left[\mathrm{Ni} $\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$

Step-by-step solution

\begin{aligned} & \mathrm{Cr}^{++}\left(3 \mathrm{ d}^4\right)=\begin{array}{|l|l|l|l|l|} \hline 1 & 1 & 1 & 1 & \\ \hline \end{array} \\ & =4 \text{ unpaired } e^{-} \\ & \operatorname{Mn}^{++}\left(3 \mathrm{ d}^4\right)= \begin{array}{|l|l|l|l|l|} \hline 1 & 1 & 1 & 1 & 1 \\ \hline \end{array} \\ & =5 \text{ unpaired } e^{-} \\ & \mathrm{Fe}^{++}\left(3 \mathrm{ d}^6\right)=<table class="qx-match-list qx-match-table" border="1" cellpadding="6" cellspacing="0"><tr><td>1L</td><td>1</td><td>1</td><td>1</td><td>1</td></tr></table> \\ & =4 \text{ unpaired } e^{-} \\ & \mathrm{Ni}^{++}\left(3 \mathrm{ d}^8\right)=<table class="qx-match-list qx-match-table" border="1" cellpadding="6" cellspacing="0"><tr><td>1h</td><td>1L</td><td>IL</td><td>1</td><td>1</td></tr></table> \\ & =2 \text{ unpaired } e^{-} \\ & \end{aligned}

\mathrm{Ni}^{++}

has minimum no. of unpaired

e^{-}$ thus this is least paramagnetic.

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