The correct order of electron affinity of the elements of oxygen family in the periodic table is

Sulphur has optimum size of all the 16th group elements and has the highest electron gain enthalpy. Oxygen due to its small size and presence of lone pairs has lesser affinity towards electrons. Thus its  electron gain enthalpy is abnormally low ,in fact least in the group. Thus ${\mathrm{\Delta H}}_{\mathrm{eg}} \mathrm{of} \mathrm{S}>\mathrm{Se}>\mathrm{Te}>\mathrm{Po}>\mathrm{O}.$