The active ingredient in commercial bleach is sodium hypochlorite, $\mathrm{NaOCI}$, which can be determined by iodometric analysis as indicated in these equations.

$$\begin{gathered} {\mathrm{OCl}}^{-}+2{\mathrm{H}}^{+}+2{\mathrm{I}}^{-}⟶{\mathrm{I}}_2+{\mathrm{Cl}}^{-}+{\mathrm{H}}_2\mathrm{O} \\ {\mathrm{I}}_2+2{\mathrm{S}}_2{\mathrm{O}}_3^{2-}⟶{\mathrm{S}}_4{\mathrm{O}}_6^{2-}+2{\mathrm{I}}^{-} \end{gathered}$$

If $1.356 \mathrm{g}$of a bleach sample requires 19.50 mL of  $0.100 \mathrm{M} {\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3=$ solution, what is the percentage by mass of $\text{ NaOCl }$ in the bleach ?