Question

The magnetic moment of $M^{x+}$ (atomic number = 25) is $\sqrt{15}BM$. The number of unpaired electrons and the value of $x$, respectively, are:

• A. 4, 3
• B. 3, 4
• C. 3, 2
• D. 5, 2

Answer 1

The correct option is B 3, 4

$M$ (Z=25) has electronic an configuration of
$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^5$
or $d^5$ means 5 unpaired electrons
$=\sqrt{5(5+2)}BM=\sqrt{35}BM$
But given magnetic moment is $=\sqrt{3(3+2)}BM$ or $=\sqrt{15}BM$
Hence, unpaired electrons =3.
$\therefore$, the oxidation number is 4 since 2 electrons are removed from $4s$ and 2 from $3d$.