Which element has the highest first ionization energy among the following?

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

Answer: (D)

Verified step by step guidance

1. Recall that the first ionization energy is the energy required to remove one mole of electrons from one mole of gaseous atoms, forming cations.
2. Understand that ionization energy generally increases across a period (left to right) in the periodic table due to increasing nuclear charge and decreases down a group due to increasing atomic radius and electron shielding.
3. Identify the positions of the given elements: Sodium (Na), Magnesium (Mg), and Aluminum (Al) are all in period 3, with Neon (Ne) at the end of the same period.
4. Recognize that Neon (Ne) is a noble gas with a full valence shell, which makes it very stable and gives it a significantly higher first ionization energy compared to the metals listed.
5. Conclude that among the elements listed, Neon (Ne) has the highest first ionization energy because it has a full octet and a strong effective nuclear charge holding its electrons tightly.