Among, $\mathrm{Sc}, \mathrm{Mn}, \mathrm{Co}$ and Cu , identify the element with highest enthalpy of atomisation. The spin only magnetic moment value of that element in its +2 oxidation state is _____ BM (in nearest integer).

Solution

$\begin{array}{|l|l|l|l|l|}\hline & Sc & Mn & Co & Cu \\\hline \begin{array}{l} \text{Enthalpy of} \\ \text{Atomisation} \\(kJ/mole)\end{array} & 326 & 281 & 425 & 339 \\\hline\end{array}$
Highest Co
$\mathrm{Co}^{+2}=(\mathrm{Ar}) 3 \mathrm{~d}^7$

$\begin{aligned}<br />& \mathrm{n}=3 \\<br>& \mu=\sqrt{15}=3.87<br />\end{aligned}$
Nearest integer $=4$

Hence, the correct answer is 4.