Find number of basic radicals among the following cations, which can form soluble complex on adding excess of  NH₃ solution: 
${\text{Cd}}^{2+} (\mathrm{aq}.), {\text{Pb}}^{2+} (\mathrm{aq}.), {\text{Ni}}^{2+} (\mathrm{aq}.), {\text{Mn}}^{2+} (\mathrm{aq}.), {\text{Zn}}^{2+} (\mathrm{aq}.), {\text{Ag}}^{+}(\mathrm{aq}.) {\text{Hg}}^{2+} (\mathrm{aq}.), {\text{Fe}}^{3+} (\mathrm{aq}.), {\text{Mg}}^{2+} (\mathrm{aq}.)$