$CN ^{- } > NH _{3} > H _{2} O > Cl ^{-}$
Wavelength absorbing light $\alpha \frac{1}{\Delta_{0}}$
Therefore, the correct order for the wavelength of absorption will be :
$\left[ Co ( CN )_{6}\right]^{3-},\left[ Co \left( NH _{3}\right)_{6}\right]^{3+},\left[ Co \left( NH _{3}\right)_{5}\left( H _{2} O \right)\right]^{3+}$ $\left[ Co \left( NH _{3}\right)_{5} Cl \right]^{+2}$