Question

what is ionisation energy​

Answer 1

$<u><b><i>In physics and chemistry, ionization energy or ionisation energy, denoted Eᵢ, is the minimum amount of energy required to remove the most loosely bound electron, the valence electron, of an isolated neutral gaseous atom or molecule$

Answer 2

It is the minimum energy required to struck out an electron from the outermost shell of an neutral,gaseous and isolated atom.