$A$ $4 : 1$ molar mixture of $He$ and $CH_4$ is kept in a vessel at $20 \ bar$ pressure. Due to a hole in the vessel,the gas mixture leaks out. What is the composition of the mixture effusing out initially?

At constant temperature,$200 \ cm^3$ of $N_2$ at $720 \ mm$ pressure and $400 \ cm^3$ of $O_2$ at $750 \ mm$ pressure are taken in a $1 \ L$ flask. What will be the total pressure of the mixture in $mm$?

Which of the following statements is incorrect?
$1$. The property of liquid drops to have minimum surface area is called surface tension.
$2$. Surface tension of liquids decreases with rise in temperature.
$3$. The $SI$ unit of surface tension is $N \ m^{-1}$.
$4$. Magnitude of surface tension is less,when there is strong attractive force between the molecules.

At $STP$,what is the actual volume occupied by the molecules of $1 \, \text{mol}$ of water vapor (i.e.,$\text{Avogadro's number} \times \text{volume of one molecule}$)?

For a liquid,the normal boiling point is $-173\,^{\circ}C$. At $2\ atm$ pressure,its boiling point should be nearly ......... $^{\circ}C$. (Given: $\Delta H_{vap} = 200\ cal/mol$,$R = 2\ cal/mol\cdot K$,$\ln 2 = 0.7$)

Mixing of two different ideal gases under isothermal reversible conditions will lead to: