Which of the following elements has the highest first ionization energy?

• A. Neon (Ne)
• B. Magnesium (Mg)
• C. Aluminum (Al)
• D. Sodium (Na)

Answer: (A)

Verified step by step guidance

1. Understand that the first ionization energy is the energy required to remove one electron from a neutral atom in the gaseous state.
2. Recall that ionization energy generally increases across a period (left to right) in the periodic table because the effective nuclear charge increases, pulling electrons closer and making them harder to remove.
3. Identify the positions of the given elements in the periodic table: Sodium (Na), Magnesium (Mg), Aluminum (Al), and Neon (Ne) are all in the same period (Period 3).
4. Compare their positions: Neon is a noble gas at the far right of Period 3, while Sodium is at the far left, followed by Magnesium and Aluminum moving rightward.
5. Conclude that Neon has the highest first ionization energy among the options because it has a full valence shell and the highest effective nuclear charge in that period, making its electrons the most tightly held.