The two isomers $\mathrm{X} \mathrm{and} \mathrm{Y}$ with the formula $\mathrm{Cr}{\left({\mathrm{H}}_2\mathrm{O}\right)}_5{\mathrm{ClBr}}_2$ were taken for experiment on depression in freezing point. It was found that one mole of X gave depression corresponding to 2 moles of particles and one mole of Y gave depression due to 3 moles of particles. The structural formulae of X and Y respectively are

Depression in freezing point is a colligative property that depends upon the number of moles of ions which a complex may give in solution.

X gave depression corresponding to 2 moles of particles. It means 2 mol of ions of a complex is present in solution, which is only possible when complex is in the form  $\left[\mathrm{Cr}{\left({\mathrm{H}}_2\mathrm{O}\right)}_4{\mathrm{Br}}_2\right]\mathrm{Cl}$   or ${\left[\mathrm{Cr}{\left({\mathrm{H}}_2\mathrm{O}\right)}_4{\mathrm{Br}}_2\right]}^{+}{\mathrm{Cl}}^{-}$ 

Similarly, $Y$ complex will be  $\left[\mathrm{Cr}{\left({\mathrm{H}}_2\mathrm{O}\right)}_5\mathrm{Cl}\right]{\mathrm{Br}}_2\text{ or }{\left[\mathrm{Cr}{\left({\mathrm{H}}_2\mathrm{O}\right)}_5\mathrm{Cl}\right]}^{+}+2{\mathrm{Br}}^{-}.$