Question

The electron affinity of the following elements can be arranged as:
(A) $Cl>O>N>C$
(B) $Cl>O>C>N$
(C) $Cl>N>C>O$
(D) $Cl>C>O>N$

Answer 1

Hint: Electron affinity represents the tendency of an atom to accept an electron and the element which will release the most amount of energy on adding an electron in its isolated gaseous atom will possess the highest electron affinity. We should remember, it increases from left to right and decreases down the group in the periodic table.

Complete step by step solution:
Let us know about what electron affinity is and how it is affected in the periodic table.
So, electron affinity is defined as, the amount of energy released when an electron is added to the outermost shell of a neutral atom or molecule in the isolated gaseous state to form a negative ion or also called an anion. Electron affinity is also referred to as electron gain enthalpy.
We should know that, on moving down the group, electron affinity tends to decrease and it increases when we move from left to right in the Periodic table.
So, out of all group halogens will have high electron affinity due to their small size and effective nuclear charge present in their nucleus. While within the period alkali metals have the least electron affinity.
Looking at the options, we have chlorine, oxygen, nitrogen and carbon.
So, chlorine belongs to the third period and seventeenth group, oxygen belongs to the second period and sixteenth group, nitrogen belongs to the second period and fifteenth group and carbon belong to the second period and fourteenth group. And we know in the same period, the affinity increases from left to right whereas, in the group, it decreases downwards. So, from the elements given, the chlorine will have the highest electron affinity as it is a halogen while the rest elements are in the same period and are arranged as carbon in first, then nitrogen and oxygen in the periodic table. So, the electron affinity will increase from carbon to oxygen.
Thus, the order will be; $Cl>O>N>C$

Hence, the correct option is (A).

Note: Remember, electron affinity decreases as we move down the group and increases when we move from left to right across the Periodic table. Electron affinity depends on the factors like the number of protons present and the size of the atom. Smaller is the size, higher is the electron affinity.