In the standardization of ${\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3$ using ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ by iodometry, the equivalent weight of ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ is:

Using the following Latimer diagram for bromine,

$$\begin{gathered} \mathrm{pH}=0 \\ {{\mathrm{BrO}}^{-}}_4\stackrel{1.82 \mathrm{V}}{⟶}{\mathrm{BrO}}_3^{-}\stackrel{1.50 \mathrm{V}}{⟶}\mathrm{HBrO}\stackrel{1.595 \mathrm{V}}{⟶}{\mathrm{Br}}_2\stackrel{1.0652 \mathrm{V}}{⟶}{\mathrm{Br}}^{-} \end{gathered}$$

the species undergoing disproportionation is: