Question

Which of the following ions has the maximum number of unpaired d-electrons?

• A. Zn${}^{2+}$
• B. Fe${}^{2+}$
• C. Ni${}^{3+}$
• D. Cu${}^{+}$

Answer 1

Answer: (B)

Fe${}^{2+}$

$F{e}^{2+}$ ion (Z=26) has electronic configuration $\left[Ar\right]3d^{6}4s^0$ . It contains 4 unpaired electrons.
$Z{n}^{2+}$ has $\left[Ar\right]3d^{10}$ electronic configuration. It contains 0 unpaired electrons.
$N{i}^{3+}$ has $\left[Ar\right]3d^7$ electronic configuration. It contains 3 unpaired electrons.
$Cu+$ has $\left[Ar\right]3d^{10}$ electronic configuration. It contains zero unpaired electrons.

Thus, the number of unpaired electrons is maximum in $F{e}^{2+}$.