50% dissociated 1M Na₂SO₄ is isotonic with 100% dissociated ____ $\mathrm{NaCl}$

$\begin{array}{l} \mathrm{i}=1-\mathrm{\alpha }+\mathrm{n\alpha }\\ {\mathrm{Na}}_2{\mathrm{SO}}_4{\mathrm{i}}_1=1-0.5+3\left(0.5\right)=2\\ \mathrm{NaCl} {\mathrm{i}}_1=1-1+2\left(1\right)\\ {\mathrm{i}}_2=2\\ \mathrm{For}\mathrm{isotonic}\mathrm{solutions},\\ {\mathrm{i}}_1{\mathrm{C}}_1={\mathrm{i}}_2{\mathrm{C}}_2\\ 2\left(1\right)=2\left({\mathrm{C}}_2\right)\\ {\mathrm{C}}_2=1\mathrm{M}\end{array}$