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

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

Answer: (B)

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, and it generally increases across a period from left to right on the periodic table due to increasing nuclear charge and decreasing atomic radius.
2. 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), with Neon being a noble gas at the far right.
3. Understand that noble gases like Neon have very stable electron configurations (full outer shells), which makes their first ionization energies significantly higher than those of metals in the same period.
4. Compare the general trend: Ionization energy increases from Sodium to Magnesium to Aluminum to Neon, because the effective nuclear charge increases and the electrons are held more tightly.
5. Conclude that Neon has the highest first ionization energy among the given elements due to its full valence shell and strong effective nuclear charge.