b
Complex with maximum number of unpaired electron will exhibit maximum attraction to an applied magnetic field

\({\left[ Zn \left( H _2 O \right)_6\right]^{2+} \rightarrow d ^{10} \text { system } \rightarrow t _{2 g }^6 eg ^4, 0 \text { unpaired } e ^{-}}\)

\({\left[ Co \left( H _2 O \right)_6\right]^{2+} \rightarrow d ^7 \text { system } \rightarrow t _{2 g }^5 eg ^2, 3 \text { unpaired } e ^{-}}\)

\({\left[ Co ( en )_3\right]^{3+} \rightarrow d ^6 \text { system } \rightarrow t _{2 g }^6 eg ^0, 0 \text { unpaired } e ^{-}}\)

\({\left[ Ni \left( H _2 O _6\right]^{2+} \rightarrow d ^8 \text { system } \rightarrow t _{2 g }^6 \text { eg }^2, 2 \text { unpaired } e ^{-}\right.}\)