Fluorine is a better oxidising agent than chlorine because $E^{\circ}_{\mathrm{F}_2/\mathrm{F}^{-}}$ is higher than $E^{\circ}_{\mathrm{Cl}_2/\mathrm{Cl}^{-}}$. It is mainly due to low bond dissociation energy, high hydration energy and lower electron gain enthalpy, non-availability of d-orbitals in valence shell, that results in higher reduction potential of$\mathrm{F}_2$ than chlorine.