GFW of $\text{NaCl}=58.5g$

Weight of solution = 500 g

Density of solution $=\text{d}=0.936g/{\text{cm}}^3$

Volume of solution, $\text{V}=\frac{\text{mass}}{\text{Density}}$

      $\text{V}=\frac{500\text{g}}{0.936\text{g}{\text{.cm}}^{-3}};\text{since,}\text{d}=\frac{m}{\text{V}}$

Formality of solution is,

  $\text{F}=\frac{\text{W}}{\text{GFW}}\times \frac{1000}{\text{V}\text{in mL}}$

$\therefore \text{Formality}=\frac{50}{58.5}\times \frac{1000}{500}\times 0.936=1.6\text{F}$