Solution:
SOLUTION
The correct order of ionisation enthalpies is
F > P > S > B
NOTE : On moving along a period ionization enthalapy increases from left to right and decreases from top to bottom in a group. But this trend breaks up in case of atom having fully or half filled stable orbitaIs.
In this case P has a stable half filled electronic configuration hence its ionisation enthalapy is greater in comparision to S. Hence the correct order is
B < S < P < F
