The correct option is D It involves high activation energy
In chemisorption, gas molecules or atoms of the adsorbate are held to the solid surface of the adsorbent by the chemical bonds.
Chemical bonds may be covalent or ionic in nature.
Since, chemisorption leads to a new compound formation at the surface of solids, it needs a high activation energy for it.
As chemisorption involves compound formation, it is generally a irreversible process.
Generally, chemisorption occurs at high temperature and leads to monolayer adsorption
Thus, statements (b) and (d) are correct.