Chemisorption requires high activation energy, so it is referred as activation adsorption. In chemisorption, adsorption first increases and then decreases with increase in temperature.

When adsorption isobar is plotted, the graph first increases and then decreases with temperature. The initial increase is due to the heat supplied, which is utilised as overcoming the activation energy barrier as required in chemisorption.

But later it decreases, due to the exothermic nature of adsorption at the equilibrium position which is illustrated in graph.

Hence, Option $\mathrm{C}$ is correct