Explain the following: Chromium is a typical hard metal while mercury is a liquid.

Which of the following has the maximum number of unpaired electrons?

 ${\mathrm{Ti}}^{2+}, {\mathrm{V}}^{3+}, {\mathrm{Fe}}^{2+}, {\mathrm{Mg}}^{2+}$

Based on the data given below, arrange ${\mathrm{Fe}}^{2+}, {\mathrm{Mn}}^{2+}$ and ${\mathrm{Cr}}^{2+}$ in the increasing order of stability of $+2$ oxidation state.

${\mathrm{E}}^{\circ }\left({\mathrm{Cr}}^{3+}\overline{){\mathrm{Cr}}^{2+}}\right)=-0.4 \mathrm{V}$, ${\mathrm{E}}^{\circ }\left({\mathrm{Mn}}^{3+}\overline{){\mathrm{Mn}}^{2+}}\right)=1.5 \mathrm{V}$, ${\mathrm{E}}^{\circ }\left({\mathrm{Fe}}^{3+}\overline{){\mathrm{Fe}}^{2+}}\right)=0.8 \mathrm{V}$