Question

The electron affinities of which group of elements are positive?
(A) VIA
(B) IVA
(C) IA
(D) Zero

Answer 1

Hint: In chemistry, the term electronic affinity or electron gain enthalpy refers to the change in energy of a neutral atom or molecule which is in the gaseous state when an extra electron is added to it to form a negative ion.

Complete step by step answer: The electron affinity of an atom or molecule generally depends upon the following factors: (a) the effective nuclear charge, (b) the size of the atom or the molecule, (c) the stability of the valence shell electronic configuration.
If the electron affinity of an atom or a molecule is low, it will mean that the extra or additional electron is very weakly bound to the nucleus in the anion of the parent atom and so the resulting anion will be very less stable. But if the electron affinity of an atom or a molecule is high, it will mean that the extra electron is strongly bound to the nucleus in the anion of the parent atom and so the resulting anion will be more stable than the parent atom.
Generally the electron affinity tends to decrease down a group from top to bottom and tends to increase along a period from left to right as the electrons added to the energy levels become closer and closer to the nucleus. Lesser the distance, more will be the attraction and hence more will be the energy released when an electron is added. Also, the more the number of valence electrons of an atom, the more easily it will tend to accept electrons. Since noble gases have fully filled orbitals, extra energy is needed to enter the electron in the next higher shell and so noble gases have very large positive electron gain enthalpies.
Since group VI A is the chalcogens, IV A is the carbon group, I A is the alkali metal group and zero group of elements are the noble gases.

So option D is correct.

Note: If energy is released when an extra electron is added to the atom or molecule, the electron affinity for that atom or molecule is assigned a negative sign while if energy is supplied to add an extra electron to the atom or the molecule, then the electron affinity for that atom or molecule is assigned a positive sign.