Chemistry

Question Analysis
This question involves comparing third ionization energies of Period 3 elements. The main focus is on distinguishing between valence and core electron removal for successive ionizations.

Key Concept Explanation
Third ionization energy is the energy required to remove a third electron from a gaseous cation (X²⁺ → X³⁺ + e⁻).
A massive increase in ionization energy occurs when the electron is removed from a filled inner core shell, rather than a valence shell.

Step-by-Step Solution
1. Write the valence electron configurations and analyze the third ionization:
Mg: [Ne] 3s² → Loses 2 valence electrons to form Mg²⁺ ([Ne], full core). The third ionization removes a core electron from Ne’s shell.
Al: [Ne] 3s²3p¹ → Loses 3 valence electrons for the third ionization (no core electron removal).
Si: [Ne] 3s²3p² → Third ionizatio...