Ionisation energy and electron affinity are defined as what?
(A).Enthalpy
(B).pontanity
(C).Equilibrium
(D).None

Hint:
Ionization energy (IE) is the energy required to remove an electron away from an atom and electron affinity is the energy released when an electron is added to a valence shell of the atom.

Complete step by step solution:
Below given are the explanations of ionisation energy and electron affinity. And on the basis of these explanations we can find the correct solution.
Ionization energy also known as the energy needed to remove a valence electron off of its molecular orbital of the atom in its neutral state. Ionization energy can be written as IE. The ionization energy of an atom decreases as we descend from a group, and increases as you go across a period, also as each molecular orbital is filled, or half filled. Atoms with lower ionization energies easily lose their valence electron(s) and become cations.
\[\mathbf{X}\text{ }\left( \mathbf{g} \right)\to {{\mathbf{X}}^{+~}}\left( \mathbf{g} \right)\text{ }+\text{ }{{\mathbf{e}}^{-}}\]
Electron affinity is the energy released when an electron is added to the atom. On the periodic table, electron affinity usually decreases down a group, and increases across a period. Electron affinity the energy changes when a neutral atom attracts an electron to become a negative ion.
Electron affinity is written as EA.
\[\mathbf{F}\left( \mathbf{g} \right)\text{ }+\text{ }{{\mathbf{e}}^{-~}}\to \text{ }{{\mathbf{F}}^{-}}\left( \mathbf{g} \right)\]
So, from the explanation we can say that ionisation energy and electron affinity are enthalpy of reaction.
So, the correct option is “A”.

Note:
The ionization energy can predict the atom's reactivity. The ionization energy is usually determined experimentally. When an electron is added to an atom, energy is given off.