Chemisorption is defined as the formation of chemical bonds between a gas molecule and a surface. Its primary characteristics are:- (1) Endothermic Process: Chemisorption is generally endothermic because energy input is necessary to break existing bonds and create new ones.- (2) Temperature Dependence: The extent of chemisorption initially rises with increasing temperature, then declines. It peaks at an optimal temperature. At excessively high temperatures, desorption of adsorbed molecules can occur due to elevated kinetic energy.- (3) Adsorption Enthalpy: The enthalpy of adsorption for chemisorption ranges from 40-400 kJ/mol. This is attributed to the formation of robust chemical bonds, resulting in significant enthalpy values.- (4) Reversibility: This assertion is inaccurate. Chemisorption is predominantly irreversible because of the strong chemical bonds formed during the process.Consequently, statement (4) is incorrect. Final Answer: \[\boxed{\text{(4) It is reversible in nature.}}\]