Here it is
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Fluorine is smaller in size than chlorine
Gaining one more electron in fluorine results in more inter electronic repulsion because of the less space available there
However, in case of chlorine size is slightly bigger so gaining one more electron is not going to create so much interelectronic repulsion as compared to fluorine
So it is more favourable of adding electron in chlorine and hence is electron affinity is more than that of fluorine,
Same reason is valid for Oxygen and sulphur
Sulphur electron affinity is more than oxygen because oxygen smaller in size and has more interelectronic repulsion than sulphur after gaining an electron