Adsorption of gas on a surface follows Freundlich adsorption isotherm. The plot of $\log \frac{\mathrm{x}}{\mathrm{m}}$ versus $\log \left(\mathrm{P}\right)$ gives a straight line with slope equal to $0.5$, then:

($\frac{\mathrm{x}}{\mathrm{m}}$ is the mass of the gas adsorbed per gram of adsorbent)