If $N_2, O_2, H_2$,and $He$ gases are filled separately in four car tubes at the same pressure,which gas will diffuse first?

Which has higher density: dry air or moist air? Why?

If some moles of $O_2$ diffuse in $18 \ sec$ and the same moles of another gas diffuse in $45 \ sec$,what is the molecular weight of the unknown gas?

If the molar ratio of two different gases is $n_1 : n_2$,then which of the following is $NOT$ necessarily equal to $n_1 : n_2$?

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 .....$atm$.

What is the $SI$ unit of rate of diffusion for a gas?