Explanation:

Chemisorption:
Chemisorption is a type of adsorption in which the adsorbate molecules are held on the surface of the adsorbent by chemical bonds. It involves the formation of new chemical bonds between the adsorbate and the adsorbent.

Statement:
The statement that is not true with respect to chemisorption is option 'D', which states that chemisorption occurs at low temperature.

Reasoning:

Depends on nature of adsorbate and adsorbent:
Chemisorption strongly depends on the nature of both the adsorbate and the adsorbent. The chemical nature and surface properties of the adsorbent determine the strength and type of chemical bonds that can be formed between the adsorbate and the adsorbent. Different adsorbates and adsorbents have different affinities for each other, leading to different rates and extents of chemisorption.

Has a large heat of adsorption:
Chemisorption is characterized by a large heat of adsorption, which is the amount of heat released or absorbed when a certain amount of adsorbate is adsorbed onto the surface of the adsorbent. This large heat of adsorption is due to the formation of chemical bonds, which involve the sharing or transfer of electrons between the adsorbate and the adsorbent.

Forms a unimolecular layer:
Chemisorption typically forms a unimolecular layer on the surface of the adsorbent. This means that the adsorbate molecules are adsorbed in a single layer on the surface, with each adsorbate molecule bonded to the adsorbent surface by chemical bonds. This mono-layer adsorption is different from physisorption, where multiple layers of adsorbate molecules can be adsorbed.

Occurs at low temperature:
The statement that chemisorption occurs at low temperature is not true. In fact, chemisorption usually occurs at high temperatures. The activation energy required for the formation of chemical bonds between the adsorbate and the adsorbent is usually high, and higher temperatures provide the necessary energy for the reaction to occur. Additionally, chemisorption is often an exothermic process, releasing heat as chemical bonds are formed.