What should be the equivalent weight of phosphorous acid,if $P=31, O=16, H=1$?

In the reaction $Ca(OH)_2 + H_3PO_4 \to CaHPO_4 + 2H_2O$,the equivalent weight of $H_3PO_4$ is:

Elements $A$ and $B$ form two compounds $B_2A_3$ and $B_2A$. $0.05$ moles of $B_2A_3$ weigh $9.0 \ g$ and $0.10$ mole of $B_2A$ weigh $10 \ g$. The atomic weights of $A$ and $B$ are:

Complete reaction of $2.0 \, g$ of calcium (at. wt. $= 40$) with excess $HCl$ produces $1.125 \, L$ of $H_2$ gas. Complete reaction of the same quantity of another metal $M$ with excess $HCl$ produces $1.85 \, L$ of $H_2$ gas under identical conditions. The equivalent weight of $M$ is closest to

If $m_1 \ g$ of metal $A$ displaces $m_2 \ g$ of another metal $B$ from its salt solution,and their equivalent weights are $E_1$ and $E_2$ respectively,how is the equivalent weight of $A$ expressed?

Write about 'Molar Mass'.