Name two phenomena that can be explained on the basis of surface tension.

At which of the following conditions is the density of a gas maximum?

At $27^{\circ} C$, a closed vessel contains a mixture of equal weights of helium (mol. wt. = $4$), methane (mol. wt. = $16$) and sulphur dioxide (mol. wt. = $64$). The pressure exerted by the mixture is $210 \ mm$. If the partial pressures of helium, methane and sulphur dioxide are $p_1, p_2$ and $p_3$ respectively, which one of the following is correct?

Calculate the partial pressure exerted by dioxygen from a mixture of $32 \ g$ $O_2$,$80 \ g$ $Ar$ (molar mass $40 \ g/mol$) and $4 \ g$ dihydrogen $(P_{\text{total}} = 10 \ bar)$. (in $bar$)

The rates of diffusion of $SO_2$, $CO_2$, $PCl_3$ and $SO_3$ are in the following order:

$A$ certain gas takes three times as long to effuse out as helium. Its molecular mass will be ........... $u$.