Which one of the following complexes will exhibit the least paramagnetic behaviour? \([ \text{Atomic number, Cr} = 24, \text{ Mn} = 25, \text{ Fe} = 26, \text{ Co} = 27 ]\)
\( [\mathrm{Cr(H_2O)_6}]^{2+} \)
\( [\mathrm{Co(H_2O)_6}]^{2+} \)
\( [\mathrm{Fe(H_2O)_6}]^{2+} \)
\( [\mathrm{Mn(H_2O)_6}]^{2+} \)