$1 g$ of activated charcoal at $STP$ undergoes monolayer of adsorption of $N{H}_{3.}$ If $1 g$ of charcoal has surface area of $2\times {10}^2{\mathrm{m}}^2$ and effective surface area of $N{H}_3$ molecule is $0.17 {\mathrm{nm}}^2,$ the millimoles of $N{H}_3$ adsorbed on $20 \mathrm{g}$ of charcoal is______. $\left[{\mathrm{N}}_{\mathrm{A}}=6.0\times {10}^{23}{\mathrm{mol}}^{-1}\right]$

The mass of gas adsorbed, $\mathrm{x}$, per unit mass of adsorbate, $\mathrm{m}$, was measured at various pressures, $\mathrm{p}.$A graph between $\log \frac{\mathrm{x}}{\mathrm{m}}$ and $\log \mathrm{p}$ gives a straight line with slope equal to $2$ and the intercept equal to $0.4771$. The value of $\frac{\mathrm{x}}{\mathrm{m}}$ at a pressure of $4 \mathrm{atm}$ is :

(Given $\log 3=0.4771$)

Given:



On the basis of data given above, predict which of the following gases shows the least adsorption on a definite amount of charcoal?