Question

Which one has greater value, second ionisation energy or third ionisation energy?

Answer 1

The 3rd ionization energy is greater than 2nd ionization energy. Because, after 2nd ionization, metal M forms M${}^{+2}$. Protons are more than electrons and nuclear charge attracts the remaining electrons to come closer. To overcome this, some extra energy is to be supplied than 2nd ionization energy.