What volume does a gas occupy at $STP$?

$A$ mixture of $0.5 \text{ mol}$ $N_2$ gas, $1.0 \text{ mol}$ $O_2$ gas and $1.5 \text{ mol}$ $H_2$ gas exerts a total pressure of $18 \text{ bar}$. Find the partial pressure of $O_2(g)$. (in $\text{ bar}$)

$A$ mixture of equal masses of ethane $(C_2H_6)$ and hydrogen $(H_2)$ is filled in an empty container at $25\,^oC$. What is the fraction of the total pressure exerted by hydrogen?

Isochores are drawn at

$A$ hydrocarbon diffuses $3\sqrt{3}$ times slower than hydrogen gas. Identify the hydrocarbon.

The rate of diffusion of a gas is directly proportional to ....