Which of the following elements would be expected to have the highest first ionization energy?

• A. K (Potassium)
• B. Na (Sodium)
• 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. Note that the elements given (K, Na, Ne, Li) are all in the same period or adjacent periods, with Ne (Neon) being a noble gas at the end of the second period.
4. Recognize that noble gases like Neon have a full valence shell, which makes their electrons more tightly bound and results in a higher first ionization energy compared to alkali metals like K, Na, and Li.
5. Conclude that among the options, Neon (Ne) will have the highest first ionization energy due to its stable electron configuration and high effective nuclear charge.