In the reaction
2NaOH + H₃PO₄ → Na₂HPO₄ + 2H₂O, the Equivalent weight of the acid is

Molar mass of phosphoric acid is 98 g/mol. Equivalent weight of phosphoric acid is calculated by dividing the molar mass of the acids with number of hydrogen ions donated by acids.

As phosphoric acid donates 2H⁺ ions, therefore its equivalent weight is:

$\mathrm{Equivalent} \mathrm{weight}=\frac{98}{2}=49$