Chemistry

Question Analysis
This question involves a Period 3 ionization energy exception. The main focus is on identifying the element with the lowest IE among P, S, and Cl and the cause of the deviation from the general increasing trend.

Key Concept Explanation
Across Period 3, IE generally increases, but S has a lower IE than P. Phosphorus has a half-filled 3p sublevel ([Ne] 3s²3p³) with one electron per orbital, minimizing repulsion.
Sulfur has [Ne] 3s²3p⁴, with one 3p orbital containing two paired electrons.
The electron-electron repulsion in this paired orbital makes it easier to remove an electron from S than from P, even though S has a higher nuclear charge.

Step-by-Step Solution
1. Recall the Period 3 IE exception: P > S (deviation from the general increasing trend).
2. Apply the...