(પરમાણુ ક્રમાંક $Cr = 24, Mn = 25, $$Fe = 26, Ni = 28$)
So, \(C r^{2+}(22)=3 d^{4}(4\) unpaired electrons)
\(M n^{2+}(23)=3 d^{5}(5\) unpaired electrons)
\(F e^{2+}(24)=3 d^{6}(4\) unpaired electrons)
\(N i^{2+}(26)=3 d^{8}(2\) unpaired electrons)
So, \(\left[N i\left(H_{2} O\right)_{6}\right]^{2+}\) exhibit minimum paramagnetic behaviour
$(I)\, [Ni(CN)_4]^{2-}\,\,\,(II)\, [NiCl_4]^{2-}\,\,\,(III)\,Ni(CO_4)\,\,\,$
$(IV)\, [Ni(H_2O)_6 ]^{2+}$