Explanation

(b)
_{25}Mn=$1s^{2}\ ,2s^{2}\ ,2p^{6}\ ,3s^{2}\ ,3p^{6}\ ,4s^{2}\ ,3d^{5}$
[table] $\upharpoonleft$ | $\upharpoonleft$ | $\upharpoonleft$ | $\upharpoonleft$ | $\upharpoonleft$ [/table]
$\because\$Number of unpaired electrons in Mn =5
$\therefore\$Magnetic moment of Mn =$\sqrt{n(n + 2)}$
$= \sqrt{5(5 + 2)} = \sqrt{35}\ = 5.91\ BM$