The flocculation value of $\mathrm{H}\mathrm{C}\mathrm{l}$ for arsenic sulphide $\mathrm{s}\mathrm{o}\mathrm{l}$ is $30 \mathrm{m}\mathrm{m}\mathrm{o}\mathrm{l}{\mathrm{L}}^{-1}$. If ${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$ is used for the flocculation of arsenic sulphide, the amount, in grams, of ${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$ in $250\mathrm{}\mathrm{m}\mathrm{l}$ required for the above purpose is ________
(molecular mass of ${\mathrm{H}}_2{\mathrm{S}\mathrm{O}}_4=\mathrm{98 }\mathrm{g}/\mathrm{m}\mathrm{o}\mathrm{l}$