1. Some basic concept of chemistry — Chemistry STD 11 Science — Question

$H_3PO_4 + Ca(OH)_2 \to CaHPO_4 + 2H_2O$ 

In this reaction

$H_{3} P O_{4} \rightarrow H P O_{4}^{2-}+2 H^{+}$

Orthophosphoric acid leaves $2$ hydrogen ions.

Hence, its valency factor is $=2$

Equivalent weight $=\frac{\text { Molecular Weight }}{2}$

Molecular weight $=1 \cdot 3+31+4 \cdot 16=98$

Therefore,

The equivalent weight is $=\frac{98}{2}=49$