Among the elements with the following atomic numbers, which one will have the highest second ionisation enthalpy?

Step-by-step solution

The atomic numbers correspond to the following elements: 11 Na 12 Mg 13 Al 14 Si The second ionisation enthalpy is the energy required to remove an electron from the unipositive cation ( M^+ ). Let us write the electronic configurations of their +1 ions: Na ^+ : 1s^2 2s^2 2p^6 (stable noble gas core) Mg ^+ : 1s^2 2s^2 2p^6 3s^1 Al ^+ : 1s^2 2s^2 2p^6 3s^2 Si ^+ : 1s^2 2s^2 2p^6 3s^2 3p^1 Removing a second electron from Na requires breaking a highly stable, fully-filled principal quantum shell (the neon core), which