Correct increasing order for the wavelengths of absorption in the visible region for the complexes of ${\text{Co}}^{3+}$ is:

Crystal field splitting energy (${\Delta }_o$) depends on the ligand strength: $en>{\text{NH}}_3>{\text{H}}_2\text{O}$.The energy of absorbed light ($E$) is inversely proportional to wavelength ($\lambda$): $E=\frac{hc}{\lambda }={\Delta }_o$.Since $en$ has the highest ${\Delta }_o$, it will absorb the shortest wavelength. ${\text{H}}_2\text{O}$ has the lowest ${\Delta }_o$ and will absorb the longest wavelength.Increasing order of ${\lambda }_{abs}$: $[{\text{Co(en)}}_3{]}^{3+}<[{\text{Co(NH}}_3{)}_6{]}^{3+}<[{\text{Co(H}}_2{\text{O)}}_6{]}^{3+}$.