Vapour density of a gas is $22$. What is its molecular mass?

What is meant by $1 \ amu$ or $1 \ u$?

In order to prepare one litre of a $1 \ N$ (normal) solution of $KMnO_4$,how many grams of $KMnO_4$ are required if the solution is used in an acidic medium for oxidation?

If $1.2 \, g$ of a metal displaces $1.12 \, L$ of hydrogen at $STP$,the equivalent weight of the metal would be:

$A$ mixture of $1.65 \times 10^{21}$ molecules of $X$ and $1.85 \times 10^{21}$ molecules of $Y$ weighs $0.688 \ g$. If the molecular mass of $Y$ is $187 \ g/mol$,what is the molecular mass of $X$?

The equivalent weight of $H_3PO_4$ in the reaction $Ca(OH)_2 + H_3PO_4 \rightarrow CaHPO_4 + 2H_2O$ is