Weight of Phosphoric acid  required to neutralise 100 g of   Magnesium hydroxide is

$$\begin{gathered} 3\mathrm{Mg}{\left(\mathrm{OH}\right)}_2+2{\mathrm{H}}_3{\mathrm{PO}}_4\to {\mathrm{Mg}}_3{\left({\mathrm{PO}}_4\right)}_2+3{\mathrm{H}}_{2}0 \\ 3 2 \\ 3\times 58\mathrm{g} 2\times 98\mathrm{g} \\ 100\mathrm{g} ?? \\ \Rightarrow \frac{100\times 2\times 98}{3\times 58}=112.6\mathrm{g} \end{gathered}$$