$(I)\, [Ni(CN)_4]^{2-}\,\,\,(II)\, [NiCl_4]^{2-}\,\,\,(III)\,Ni(CO_4)\,\,\,$
$(IV)\, [Ni(H_2O)_6 ]^{2+}$
$\left[ NiCl _4\right]^{2-}$ and $\left[ Ni ^2\left( H _2 O \right)_6\right]^{2+}$ contain 2 unpaired electrons each. Thus they are paramagnetic and will be attracted by the magnetic field.
In $\left[ Ni ( CN )_4\right]^{2-}$ and $\left[ Ni ( CO )_4\right]$, all the electrons are paired. Hence, they are diamagnetic substances and are not attracted by the magnetic field.
$(i)\, Pt(SCN)_2 · 3PEt_3$
$(ii)\, CoBr · SO_4 · 5NH_3$
$(iii)\, FeCl_3 · 6H_2O$