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(i)- Electron gain enthalpy of halogens
(ii) Electronegativity of halogens.

Explanation

(i) Electron gain enthalpy : Halogens have maximum negative electron gain enthalpy in the corresponding periods due to fact that the atoms of these elements have only one electron less than noble gas configurations.
The electron gain enthalpy becomes less negative down the group. However, the negative electron gain enthalpy of fluorine is less than that of chlorine. It is due to small size of fluorine atom. As a result, there are strong interelectronic repulsions in the relatively small 2p-orbitals of fluorine and thus, the incoming electron does not experience much attraction.
Electron gain enthalpy : F < CI > Br > I
(ii) Electronegativity : Halogens are highly electronegativity elements. This is due to its small size and high nuclear charge. Fluorine is the most electronegative element in the periodic table.
The electronegativity of the elements decreases down the group which indicates decrease in non-metallic character.
Order of Electronegativity : F > CI > Br > I