$1 \ amu$ is equal to

The equivalent weights of $H_3PO_4$ in the following reactions are respectively:
$H_3PO_4 + OH^{-} \rightarrow H_2PO_4^- + H_2O$
$H_3PO_4 + 2OH^{-} \rightarrow HPO_4^{2-} + 2H_2O$
$H_3PO_4 + 3OH^{-} \rightarrow PO_4^{3-} + 3H_2O$

The molecular weight of a tribasic acid is $M$. What will be its equivalent weight?

Vapour density of a metal chloride is $66$. Its oxide contains $53\%$ metal. The atomic weight of the metal is

In chlorine,the isotopes $^{35}Cl$ and $^{37}Cl$ are present in the ratio $3:1$. Calculate the atomic mass of chlorine. (in $amu$)

The equivalent weight of $Zn(OH)_2$ in the following reaction is equal to its: $Zn(OH)_2 + HNO_3 \to Zn(OH)(NO_3) + H_2O$