Question

Different elements exist in different physical states.However,only gaseous state is taken into consideration for an elements for defining IP or EA.Give reasons.

Answer 1

Electron affinity EA and Ionization potential IP or ionization energy IE are defined and measured in the gaseous state only. 

EA is the energy released when an electron is added to a neutral gaseous atom.  IE is the energy that is to be given to an atom to release an electron from a neutral atom of an element.

These are defined for the gaseous state as in gaseous state the atoms and molecules are far away and there is no bonding or attraction between them.  In solid or liquid state, the atoms are so close that there are bonds between them.  Hence the values of ionization energy or electron affinity change and we cannot find them accurately.