Question

What is ionisation energy

Answer 1

Ionization energy is the energy required to remove an electron from a gaseous atom or ion. The first or initialionization energy or Ei of an atom or molecule is the energyrequired to remove one mole of electrons from one mole of isolated gaseous atoms or ions.

Answer 2

The enthalpy change that occurs when an electron is removed from an outermost shell of an atom is called  ionization energy or  ionization enthalpy