Iodine and chlorine react with hypo in different ways as follows
 $\begin{array}{l}2{\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3+{\mathrm{I}}_2\to 2\mathrm{NaI}+{\mathrm{Na}}_2{\mathrm{S}}_4{\mathrm{O}}_6\\ {\mathrm{Cl}}_2\left(\mathrm{g}\right)+{\mathrm{S}}_2{\mathrm{O}}_3^{2-}\to {\mathrm{SO}}_4^{2-}+{\mathrm{Cl}}^{-}+\mathrm{S}\end{array}$
Suppose 50 mL of 0.01 M ${\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3$ solution and $5\times {10}^{-4}$  mol of ${\mathrm{Cl}}_2$ are allowed to react according to the above equation. Hypo is also used in photography to dissolve $\mathrm{AgBr}$ forming a complex compound
 $2{\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3+\mathrm{AgBr}\to {\mathrm{Na}}_2\left[\mathrm{Ag}{\left({\mathrm{S}}_2{\mathrm{O}}_3\right)}_2\right]+\mathrm{NaBr}$