Why chlorine is not the most powerful oxidising agent inspite of its highest value of electron gain enthalpy?

Explanation

Oxidising property of an halogen depends on three factor 1) electron gain enthalpy 2) bond dissciation energy and 3) the hydration enthalpy.
In presence of 3d-shell in Cl, it can accommodate its electron with less repulsion and `Cl_2` requires higher energy to break Cl-Cl bond. Further, the size of Cl is comparatively larger and hence it has low charge density. This leads to the low hydration enthalpy of Cl -atom. Therefore, despite of having highest electron gain enthalpy chlorine is not the most powerful oxidising agent