Standard reduction potentials of the half reactions are given below:${\text{F}}_{2(\text{g})}+2e^{-}\to 2{\text{F}}_{(\text{aq})}^{-};E^{\circ }=+2.85\text{V}$${\text{Cl}}_{2(\text{g})}+2e^{-}\to 2{\text{Cl}}_{(\text{aq})}^{-};E^{\circ }=+1.36\text{V}$${\text{Br}}_{2(\text{g})}+2e^{-}\to 2{\text{Br}}_{(\text{aq})}^{-};E^{\circ }=+1.06\text{V}$${\text{I}}_{2(\text{g})}+2e^{-}\to 2{\text{I}}_{(\text{aq})}^{-};E^{\circ }=+0.53\text{V}$ The strongest oxidising and reducing agents respectively are:

* Oxidising Agent: A species that gets reduced. The higher the positive $E^{\circ }$ value, the greater the tendency to get reduced. ${\text{F}}_2$ ($E^{\circ }=+2.85\text{V}$) is the strongest oxidising agent.Reducing Agent: A species that gets oxidised. The lower the $E^{\circ }$ reduction value (or higher the oxidation potential), the greater the tendency of its reduced form to get oxidised. Since ${\text{I}}_2/{\text{I}}^{-}$ has the lowest reduction potential ($+0.53\text{V}$), ${\text{I}}^{-}$ has the greatest tendency to lose electrons and act as the strongest reducing agent.