d
\(\Delta_0\) value is directly proportional to energy and inversely related to the wavelength. Also, more the ligand is a strong field ligand More will be the value of \(\Delta_{\circ}\) and lower will be its wavelength. Among the given complexes the strength of ligands are \(Br ^{-}< H _2 O <\) en.Since the emitted colours are red, green, blue the absorbed colours must be green,red,orange. Hence the compound \(\left[ M \left( H _2 O \right)_6\right]^{2+},\left[ M ( en )_3\right]^{2+},\left[ M ( Br )_6\right]^{4-}\) are blue red and green respectively.