If $1.2 \ g$ of a metal displaces $1.12 \ L$ of hydrogen at $NTP$,what is the equivalent weight of the metal?

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

In a copper sulfate solution,$3.2 \ g$ of copper is displaced by $2.8 \ g$ of iron. If the equivalent mass of iron is $28$,what is the equivalent mass of copper?

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

Oxygen contains $90\%$ of $^{16}O$ and $10\%$ of $^{18}O$. Its atomic mass is

The $2\,N$ aqueous solution of $H_2SO_4$ contains