In Van der Waals equation $\left( P + \frac{a}{V^2} \right)(V - b) = RT$,what do $a$ and $b$ represent?

In the absence of intermolecular forces of attraction,the observed pressure $P$ will be

$A$ container is divided into two equal parts $I$ and $II$ by a partition with a small hole of diameter $d$. The two parts are filled with the same ideal gas,but held at temperatures $T_{I} = 150 \, K$ and $T_{II} = 300 \, K$ by connecting them to heat reservoirs. Let $\lambda_{I}$ and $\lambda_{II}$ be the mean free paths of the gas particles in the two parts,such that $d \gg \lambda_{I}$ and $d \gg \lambda_{II}$. Then,the ratio $\lambda_{I} / \lambda_{II}$ is close to:

An ideal gas in a closed container is slowly heated. As its temperature increases,which of the following statements are true?
$(A)$ The mean free path of the molecules decreases.
$(B)$ The mean collision time between the molecules decreases.
$(C)$ The mean free path remains unchanged.
$(D)$ The mean collision time remains unchanged.

Internal energy of a non-ideal gas depends on ..........

Calculate the mean free path and relaxation time for a gas with a mean speed $\langle v \rangle = 485 \ m/s$. Assume standard conditions $(STP)$ where the number density $n \approx 2.7 \times 10^{25} \ m^{-3}$ and molecular diameter $d = 2 \ \mathring{A}$.