Second electron affinity of sulfur and oxygen
The electron affinity of an atom or molecule is defined as the amount of energy released when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion.

It is the tendency of an atom to gain electron. It is numerically equal to the negative of electron gain enthalpy.

Although fluorine has the highest electronegativity, chlorine has the highest electron affinity and this is because the considerable repulsion in the tightly packed $2p$ subshell of fluorine.

While electron gain enthalpy is enthalpy change when an isolated gaseous atom attain an electron to form a monovalent gaseous anion.

Chlorine ($\ce{Cl}$) has more negative electron gain enthalpy than fluorine the reason is same  as above.



Source:

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