Why is it important to have a clean surface in surface studies?

$A$ mixture of substances $A, B, C, D$ is subjected to column chromatography. The degree of adsorption is in the order of $D > B > C > A$. The column is eluted with a suitable solvent. Identify the correct statement with respect to the separation of the mixture.

Which of the following is true in respect of chemical adsorption?

The plot of $\log(\frac{x}{m})$ against $\log P$ is a straight line inclined at an angle of $45^{\circ}$. When the pressure is $0.5 \ atm$ and the Freundlich parameter $(K)$ is $10$,the amount of solute adsorbed per gram of adsorbent will be $(\log 5 = 0.699)$ .......... $g$.

Which of the following statements is not applicable to chemisorption?

Which among the following is true for chemisorption?