The possible number of isomers for the complex $\left[{\mathrm{MCl}}_2{\mathrm{Br}}_2\right]{\mathrm{SO}}_4$ is:

The colour of the coordination compounds depends on the crystal field splitting. What will be the correct order of absorption of the wavelength of light in the visible regions for the complexes:

${\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_6\right]}^{3+}, {\left[\mathrm{Co}{\left(\mathrm{CN}\right)}_6\right]}^{3-}, {\left[\mathrm{Co}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{3-}$