What is Adsorption?

Question

$\begin{array}{1 1} \text{Adsorption is the variation in the amount of gas adsorbed by the adsorbate with pressure at constant temperature.} \\ \text{(b)Adsorption is the variation in the amount of gas adsorbed by the adsorbent with pressure at constant temperature.} \\ \text{(c) Adsorption is defined as the deposition of molecular species onto the surface.} \\ \text{(d) Adsorption is a chemical or physical phenomenon in which the molecules, atoms and ions of the substance getting adsorbed enters into the bulk phase} \end{array}$