The flocculation value of $HCl$ for arsenic sulphide sol is $30 m mol{ L}^{-1}$. If $H_2{SO}_4$ is used for the flocculation of arsenic sulphide, the amount, in grams, of $H_2{SO}_4$ in $250ml$ required for the above purpose is

(molecular mass of $H_2{SO}_4=98 g/mol$ )

The flocculation value of $HCl$ for arsenic sulphide sol is $30 m mol{ L}^{-1}$ . If $H_2{SO}_4$ is used for flocculation, then the concentration will be 15 m mol L^-1 $\left(\frac{30 \mathrm{m} \mathrm{mol} {\mathrm{L}}^{-1}}{2}\right)$ because each $H_2{SO}_4$ gives $2H^{+}$.

In $250ml$ concentration, moles present will be equal to $\frac{15}{4}\times {10}^{-3} mol$.

Therefore,

$\frac{w_{H_2{SO}_4}}{98}=\frac{15}{4}\times {10}^{-3}$

$w_{H_2{SO}_4}=\frac{15}{4}\times 98\times {10}^{-3}$

$=0.3675gm$

Hence the weight of $H_2{SO}_4$ will be equal to $0.3675gm$.