$\underbrace{ CO > CN ^{-}> NO _{2}^{-}> NH _{3}>}_{\text{Strong field ligand cause pairing of electrons}}$
$\underbrace{ H _{2} O > F ^{-}> Cl ^{-}> Br ^{-}> I ^{-}}_{\text {Weak field ligand does not cause pairing }}$
$n=0$ (diamagnetic)
$d s p^{2}$ hybridisation, low spin complex.
$Ni ^{2+}$ in presence of weak ligand $Cl ^{-}$
$n=2$, paramagnetic
$s p^{3}$, hybridisation, high spin complex.
$Co^{2+}$ in presence of weak ligand $Cl ^{-}$
$n=3$, paramagnetic, $s p^{3}$ hybridisation
$Co ^{2+}$ in presence of weak ligand $F ^{-}$
$n=5$, paramagnetic, $s p^{3} d^{2}$ hybridisat
