[પ.ક્ર.: $Cr= 24,\,Mn= 25, \,Fe= 26, \,Co= 27$]
$C r^{2+}$ and $F e^{2+}$ has same number of unpaired electrons
$C r^{2+}=>3 d^{4}$ four unpaired electrons
$F e^{2+}=>3 d^{6}$ four unpaired electrons
$1.$ $[Co(NH_3)_5NO_2]Cl_2$ અને $[Co(NH_3)_5ONO]Cl_2$ $-$ બંધનીય
$2.$ $[Cu(NH_3)_4] [PtCl_4]$ અને $[Pt(NH_3)_4] [CuCl_4]$ $-$ સવર્ગ
$3.$ $[Pt(NH_3)_4Cl_2]Br_2$ અને $[Pt(NH_3)_4Br_2]Cl_2$ $-$ આયનીકારક