Question

1. Which one of the following arrangements
represents the correct order of electron gain
enthalpy (with negative sign) of the given atomic
species :-
(1) F< Cl<O<S (2) S<O< Cl< F
(3) O <S< F< Cl (4) Cl< F<S< 0​

Answer 1

Answer:

Halogens have high electron affinity because by gaining an electron they achieve the stable noble gas configuration. Also, it increases along a period and decreases on moving down a group, but the value of electron gain enthalpies for the elements are Cl = 349, F = 333, S = 200, O = 142.

The E.A. of F is less than chlorine and that of  O is less than S, because fluorine & oxygen atoms are smaller in size, so the incoming electron is added to space already crowded with electrons and will thereby experience strong repulsion.

hope it helps :p