The element having higher electron affinity is:
(A) fluorine
(B) nitrogen
(C) chlorine
(D) oxygen

Hint: Atoms having unfilled shells are unstable, and to achieve the stability they usually make chemical bond either by gaining or losing electrons showing different phenomena like electron affinity, electronegativity, electron gain enthalpy and ionization energy.

Complete step by step solution:
We have two types of atoms: stable and unstable,
Stable or neutral atoms are usually unreactive, but the unstable ones do make chemical bonds with different atoms by gaining, losing and sharing of electrons,
Due to the formation of these chemical bonds we have several phenomena related to the energy,
One of them is electron affinity:
The electron affinity of an atom or molecule is defined as the amount of energy released when an electron is attached to a neutral atom or molecule in the gaseous state to form a negative ion.
While referring to the modern periodic table, halogens have higher electron affinity,
The electrons of halogens are since farther away, they are less attracted towards the nucleus and release less energy while reacting,
But among halogens fluorine should have the highest electron affinity, but it is not the case as fluorine has a small size, so instead of fluorine chlorine has the highest electron affinity.
The electron affinity of the fluorine is less than chlorine because the size of fluorine is too small as size decreases from left to right inside the period, whereas chlorine has a larger size to accommodate electrons hence electron affinity of chlorine is more than fluorine
So, the element having the highest electron affinity is chlorine.

Therefore, option (C) is correct.

Note: The electron affinity of an element depends upon electron gain enthalpy. It is the amount of heat energy released or absorbed when an electron is accepted. The element having more negative electron gain enthalpy will have more electron affinity.