Between $NH_3$ and $N_2$,which one has a higher value of $(i) \ a$ and which one has a higher value of $(ii) \ b$? (Where $a$ and $b$ are van der Waals constants.)

For real gases,the relation between $p$,$V$,and $T$ is given by the van der Waals equation:
$(p + \frac{an^2}{V^2})(V - nb) = nRT$
Where $a$ and $b$ are van der Waals constants,$nb$ is approximately equal to the total volume of the molecules of a gas,and $a$ is the measure of the magnitude of intermolecular attraction.
$(i)$ Arrange the following gases in the increasing order of $b$. Give reason: $O_2, CO_2, H_2, He$
$(ii)$ Arrange the following gases in the decreasing order of magnitude of $a$. Give reason: $CH_4, O_2, H_2$

The values of the van der Waals constant $a$ for gases $O_2, N_2, NH_3$,and $CH_4$ are $1.360, 1.390, 4.170$,and $2.253 \ L^2 \ atm \ mol^{-2}$ respectively. Which gas can be liquefied most easily?

Gas deviates from ideal gas nature because molecules

Assertion : Compressibility factor $(Z)$ for non-ideal gases can be greater than $1$.
Reason : Non-ideal gases always exert higher pressure than expected.

Under which conditions do intermolecular forces become effective?