What volume does a gas occupy at $STP$?

At $T(K)$,a gaseous mixture containing $H_2, He$ and $O_2$ exerted a pressure of $1 \ bar$. The weight percentage of $H_2$ and $He$ is $20$ and $16$ respectively. The partial pressure (in bar) of $H_2, He$ and $O_2$ is respectively

At $100\,^oC$ and $1\, atm$ pressure,the density of liquid water is $1.0\, g\, cm^{-3}$ and the density of water vapor is $0.0006\, g\, cm^{-3}$. What is the volume occupied by water molecules in $1\, L$ of steam at the same temperature in $cm^3$?

$A$ mixture of $N_2$ and $Ar$ gases in a cylinder contains $7 \ g$ of $N_2$ and $8 \ g$ of $Ar$. If the total pressure of the mixture of gases in the cylinder is $27 \ bar$,the partial pressure of $N_2$ is $......... \ bar$.
[Use atomic masses (in $g \ mol^{-1}$) : $N=14, Ar=40$]

In water saturated air,the mole fraction of water vapour is $0.02$. If the total pressure of the saturated air is $1.2 \; atm$,the partial pressure of dry air is .....$atm$.

Normal boiling point of water is $373 \ K$ (at $760 \ mm$). Vapour pressure of water at $298 \ K$ is $23 \ mm$. If the enthalpy of evaporation is $40.656 \ kJ/mole$,the boiling point of water at $23 \ mm$ pressure will be ............. $K$.