Which of the following species is/are paramagnetic?
${\mathrm{Fe}}^{2+},{\mathrm{Zn}}^0,{\mathrm{Hg}}^{2+},{\mathrm{Ti}}^{4+}$

The outermost electronic configuration of Fe is
$$\begin{gathered} \mathrm{Fe}=\left[\mathrm{Ar}\right]3{\mathrm{d}}^{6}4{\mathrm{s}}^2 \\ {\mathrm{Fe}}^{2+}=\left[\mathrm{Ar}\right]3{\mathrm{d}}^{6}4{\mathrm{s}}^0 \end{gathered}$$
 

$$\begin{gathered} \text{ Since }{\mathrm{Fe}}^{2+}\text{ has }4\text{ unpaired electrons it is paramagnetic in nature. } \\ \mathrm{Zn}=\left[\mathrm{Ar}\right]3{\mathrm{d}}^{10}4{\mathrm{s}}^2\dots \text{ no unpaired }{\mathrm{e}}^{-} \\ {\mathrm{Hg}}^{2+}=\left[\mathrm{Ar}\right]4{\mathrm{f}}^{14}5{\mathrm{d}}^{10}\dots \text{ no unpaired }{\mathrm{e}}^{-} \\ {\mathrm{Ti}}^{4+}=\left[\mathrm{Ar}\right]3{\mathrm{d}}^{0}4{\mathrm{s}}^0\dots \text{ no unpaired }{\mathrm{e}}^{-} \end{gathered}$$