HELLO,
The answer is Sulphur and i will give the reasons below.
Here Oxygen is most electronegative element and Sulphur is also the same part of the group
I will give the values of electronegativity below
O = 140Kj/mol
S = 200 Kj/mol
P = 72 Kj/mol
N = 7 Kj/mol
beneath the values i will give the reasons also
As you know that electron affinity is negative values
Size of oxygen is smaller than sulphur
so incoming electron feel repulsion for O than S
So electron affinity ,S>O
Same is the reason for N and P as they are same group i,e 17 so electron affinity must be less than sulphur
THANK YOU