Which of the following will have the most negative electron gain enthalpy and which the east negative? (P, S, CI, F). Explain your answer.

Explanation

Negative value of electron gain enthalpy increases along a period and decreases down the group. Elements of 2nd period like F have lesser electron gain of energy than the corresponding element of third period. This is because of smaller size and hence greater repulsion in case of F as compared to Cl. Thus correct order of electron gain enthalpy is `PltSltFltCl` i.e., electron gain enthalpy is most negative for chlorine and less negative for phosphorus