When ${\mathrm{CS}}_2$ layer containing both ${\mathrm{Br}}_2$and ${\mathrm{I}}_2$ (2 : 1) is shaken with excess chlorine $\left({\mathrm{Cl}}_2\right)$ water, the violet colour due to ${\mathrm{I}}_2$disappears and a pale yellow colour appears in the solution. The disappearance of Violet colour and appearance of pale yellow colour is due to the formation of :

In chlorine water test for iodine and bromine :-

$\begin{array}{r}{\mathrm{Br}}_2\uparrow +{\mathrm{Cl}}_2\uparrow \rightleftharpoons 2\mathrm{BrCl}\end{array}$(pale yellow solution)

${\mathrm{Br}}_2+{\mathrm{CS}}_2/\mathrm{CH}{\mathrm{Cl}}_3⟶{\mathrm{Br}}_2$ (in organic layer reddish- brown in color )

$2{\mathrm{I}}^{-}+{\mathrm{a}}_2⟶2{\mathrm{a}}^{-}+{\mathrm{I}}_2\uparrow$

${\mathrm{I}}_2+{\mathrm{CHCl}}_3⟶{\mathrm{I}}_2$   (in organic layer violet in  color )

When we add the excess of ${\mathrm{Cl}}_2$ water

${\mathrm{Br}}_2\uparrow +\mathrm{Cl} 2 \uparrow \to \underset{\mathrm{yellow}}{2\mathrm{BrCl} }$

${{\mathrm{I}}_3}^{- }+8{\mathrm{Cl}}_2+9{\mathrm{H}}_2\mathrm{O}⟶3{\mathrm{IO}}_3^{-}+16{\mathrm{Cl}}^{-}+18{\mathrm{H}}^{+}$