Question

what is ionization energy?

Answer 1

Ionization energy is simple terms can be described as a measure of the difficulty in removing an electron from an atom or ion or the tendency of an atom or ion to surrender an electron. The loss of electron usually happens in the ground state of the chemical species.

Alternatively, we can also state that ionization or ionisation energy is the measure of strength (attractive forces) by which an electron is held in a place.

Answer 2

The energy required to remove an electron from the outermost orbit or shell of neutral gaseous atom is called ionization energy.