Which of the following electronic configuration would you expect to have the lowest ionization energy and why?
a)1S2, 2S2, 2P6
b) 1S2, 2S2, 2P5
c) 1S2, 2S2, 2P6,3S1

Ans: As we know the elements having half-filled and full filled electronic configuration are stable and they need more energy to move the electron and have higher ionization energy. So, (a) and (c) have higher ionization energy because they have fulfilled and half-filled electronic configuration respectively and (b) has lowest ionization energy due to having unstable electronic configuration.