In case of diatomic molecules (X2) of halogens the bond dissociation energy decreases in the order : Cl2>Br2>F2>I2 The oxidizing power, electronegativity and reactivity decrease in the following order: F2>Cl2>Br2>I2 Electron gain enthalpy fo halogens decreases in the following order :
Cl2>F2>Br2>I2 The low value of electron gain enthalpy of fluorine is due to small size of fluorine atom.