(i) \(O\) and \(F\) are present in the same period of the periodic table. An \(F\) atom has one proton and one electron more than \(O\) and as an electron is being added to the same shell, the atomic size of \(F\) is smaller than that of \(O\). As \(F\) contains one proton more than \(O\), its nucleus can attract the incoming electron more strongly in comparison to the nucleus of \(O\) atom. Also, \(F\) needs only one more electron to attain the stable noble gas configuration.
Hence, the electron gain enthalpy of \(F\) is more negative than that of \(O\).
(ii) \(F\) and \(Cl\) belong to the same group of the periodic table. The electron gain enthalpy usually becomes less negative on moving down a group. However, in this case, the value of the electron gain enthalpy of \(Cl\) is more negative than that of \(F\). This is because the atomic size of \(F\) is smaller than that of \(Cl\). In \(F\), the electron will be added to quantum level \(n\) = \(2\), but in \(Cl\), the electron is added to quantum level \(n\) = \(3\). Therefore, there are less electron repulsions in \(Cl\) and an additional electron can be accommodated easily.
Hence, the electron gain enthalpy of \(Cl\) is more negative than that of \(F\).