Step 1: Understanding the Question:
The question identifies which property does not belong to chemical adsorption (chemisorption).
Step 2: Detailed Explanation:
1. Chemisorption is highly specific as it involves chemical bond formation between adsorbent and adsorbate.
2. The heat of adsorption is high ($80 - 400$ kJ/mol or sometimes reported as $40 - 400$ kJ/mol depending on the text) because of bond formation.
3. It results in a unimolecular layer because once the surface sites are occupied by chemical bonds, no more adsorbate can bond directly to the surface.
4. It is generally irreversible because bond breaking requires high energy.
5. Statement (C) describes physisorption, not chemisorption.
Step 4: Final Answer:
Formation of a multimolecular layer is characteristic of physisorption, not chemisorption.