Account for the following: Among the halogens `F_2` is the strongest oxidising agent.

Explanation

All halogens are oxidising agents, however, reactivity decrcases down the group, thus fluorine is the strongest oxidising agent and iodine is the weakest. This is mainly due to the fact that electron gain enthalpy becomes less negative as we move down the group. However, as we know electron gain enthalpy of fluorine is unexpectedly less negative as compared to chlorine. Despite this fact fluorine `(F_2)` is a stronger oxidising agent than chlorine `(Cl_2)` as is evident from the fact that sluorine can oxidisc other halide ions even in solid state.
` F_2 (g) + 2NaCl (s) to 2NaF (s) +Cl_2 (g)`
It is due to the following two factors : (i) Enthalpy of dissociation of F-F bond is less than CI -Cl bond. (ii) Enthalpy of hydration of `F^(-) `ion is more than `Cl^(-)` ion.
`1/2 X (g) overset(1/2 Delta D_("diss")^(0))to X (g)`
`X (g) + e^(-) overset(Delta H_(eg))toX^(-) (g)`
`X^(-) (g) + aq overset(Delta H_("hyd")^(0))to X^(-) (aq)`