Electron configurations determine orbital of first ionization in period 3 Steps:

• Period 3 elements (Na to Ar) fill 3s then 3p orbitals: Na ([Ne] 3s¹), Mg (3s²), Al (3s²3p¹) to Ar (3s²3p⁶).
• First ionization removes the highest-energy electron.
• For Na and Mg, this is from 3s orbital.
• For Al, Si, P, S, Cl, Ar, it is from 3p orbital. Why B is correct:
• B lists Al, Si, P, Cl, Ar, matching elements (Al to Ar, excluding S which is also 3p but omitted in options) where first ionization removes a 3p electron, per Aufbau principle. Why the others are wrong:
• A includes Mg, where electron is removed from 3s, not p.
• C includes Mg (3s) and excludes Al, S, Ar (all 3p).
• D excludes Al, S, Cl, Ar (all 3p removals).

Final answer: B