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

• A. Na (Sodium)
• B. K (Potassium)
• C. Ne (Neon)
• D. Li (Lithium)

Answer: (C)

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. Recall that ionization energy generally decreases down a group (top to bottom) because the outer electrons are farther from the nucleus and are shielded by inner electrons, making them easier to remove.
4. Identify the positions of the elements: Na (Sodium) and K (Potassium) are in Group 1, with K below Na; Li (Lithium) is also in Group 1 but above Na; Ne (Neon) is a noble gas in Group 18, at the end of the same period as Na.
5. Conclude that Neon (Ne), being a noble gas with a full valence shell and located at the right end of the period, has the highest first ionization energy among the given elements.