Amongst the following elements (whose electronic configurations are given below), the one having the highest ionisation energy is.
Option 1 and 3 are not stable electronic configuration due to absence of half-filled or fully-filled p-orbitals.
Option 2 and option 4 have half-filled p-orbitals. Therefore, they are more stable.
Among option 2 and option 4, the ionisation energy will be higher for configuration at option 2 is more stable than option 4 because of smaller atomic size.
Hence option 2 is correct.