The correct trend in the first ionization enthalpies of the elements in the 3^ rd period of periodic table is :

Step-by-step solution

First ionization enthalpy generally increases across a period due to increasing nuclear charge and decreasing atomic radius. However, exceptions occur based on electron configuration stability. For 3rd period elements, the approximate ionization enthalpy values are: Al (578), Si (787), P (1012), S (1000), Cl (1251) kJ/mol. (1) Al has lower IE than Si because removing 3p¹ is easier than removing one electron from 3p². (2) S has slightly lower IE than P despite being to the right because P has a half-filled p-orbital