Question

Assertion: Electron affinity of noble gas elements is zero.
Reason: Electron affinity reflects the ability of an atom to accept an electron. It is the energy change that occurs when an electron is added to a gaseous atom. Atoms with stronger effective nuclear charge have greater electron affinity.
Choose the correct option below.
(A) both assertion and reason are true and the reason is the correct explanation of the assertion.
(B) both assertion and reason are true but reason is not a correct explanation of the assertion.
(C) assertion is true but reason is false
(D) the assertion and reason both are false.

Answer 1

Hint: : Electron is accepted by the isolated atoms when there is deficiency of electrons, when the octet is incomplete , then electron is taken up by the isolated gaseous atom to complete its octet, which in turn increases its stability.

Complete step by step answer:
Electron affinity is defined as the change in energy( in kJ/mol) of a neutral atom (in the gaseous phase) when an electron is added to the atom to form a negative ion. In other words, the neutral atoms’s likelihood of gaining an electron. When an electron is added to a neutral atom ( i.e., first electron affinity) energy is released, thus, the first electron affinities are negative. However, more energy is required to add an electron to a negative ion (i.e., second electron affinity) which overwhelms any release of energy from the electron attachment process and hence, second electron affinities are positive.
Electron affinity of noble gas is near zero. Noble gas has completely filled valence shells and stable octets. It does not accept electrons easily as they have no deficiency, also adding electrons produces repulsion between the electrons. So, the correct answer is “Option A”.

Note: Electron affinity increases upward for the groups and from left to right across periods of a periodic table because the electrons added to energy levels become closer to the nucleus. Chlorine atom of p-block has the highest electron affinity.