Gram Equivalent weight of  Phosphoric acid in the reaction,  $2{\mathrm{H}}_3{\mathrm{PO}}_4+\mathrm{Ca}{\left(\mathrm{OH}\right)}_2 \to \mathrm{Ca}{\left({\mathrm{H}}_2{\mathrm{PO}}_4\right)}_2+2{\mathrm{H}}_2\mathrm{O}$  is

$$\begin{gathered} 2{\mathrm{H}}_3{\mathrm{PO}}_4+\mathrm{Ca}{\left(\mathrm{OH}\right)}_2 \to \mathrm{Ca}{\left({\mathrm{H}}_2{\mathrm{PO}}_4\right)}_2+2{\mathrm{H}}_2\mathrm{O}; \\ {\mathrm{H}}_3{\mathrm{PO}}_4 \to {\mathrm{H}}_2{\mathrm{PO}}_4^{-} \\ \mathrm{Only} \mathrm{one} \mathrm{hydrogen} \mathrm{atom} \mathrm{is} \mathrm{replaced}. \\ \mathrm{GEW}=\frac{\mathrm{GMW}}{1} \end{gathered}$$