In \(\left[\mathrm{Ni}(\mathrm{CO})_4ight]\), the \(\mathrm{Ni}^{\circ}\left(3 \mathrm{~d}^8 4 \mathrm{~s}^2ight)\) atom undergoes \(\mathrm{sp}^3\) hybridization and contains 0 unpaired electrons.
In \(\left[\mathrm{Co}\left(\mathrm{NH}_3ight)_4\left(\mathrm{NO}_2ight)_2ight]^{+}\), the \(\mathrm{Co}^{3+}\left(3 \mathrm{~d}^6ight)\) atom undergoes \(\mathrm{d}^2 \mathrm{sp}^3\) hybridization and contains 0 unpaired electrons.
In \(\left[\operatorname{Ag}(\mathrm{CN})_2ight]^{-}\), the \(\operatorname{Ag}^{+}\left(\mathrm{d}^{10}ight)\) atom contains o unpaired electrons.
In \(\left[\mathrm{CuBr}_4^1ight]^{2-}\), the \(\mathrm{Cu}^{2+}\left(3 \mathrm{~d}^9ight)\) atom undergoes \(\mathrm{sp}^3\) hybridization and contains 1 unpaired electrons. hence, it has maximum number of unpaired electrons.
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