Which of the following will have the most negative electron gain enthalpy and which the least negative ? `F,P,S,CI`.

Explanation

Electron gain enthalpy generally becomes more negative across a period as we move from the left to the right. Within a group,m electron gain entahlpy becomes less negative down a group. However, adding an electron to the `2p`-orbital leads to the greater repulsion than adding an electron to the larger `3p`-orbital. Hence, the element with the most negative electron gain enthalpy is chlorine, and the one with the least negative electron gain enthalpy is phosphorus.