Which of the following elements has the highest ionization energy?

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

Answer: (A)

Verified step by step guidance

1. Recall that ionization energy is the energy required to remove an electron from a gaseous atom or ion. It generally increases across a period (left to right) and decreases down a group (top to bottom) in the periodic table.
2. Identify the positions of the given elements in the periodic table: Li (Group 1, Period 2), Na (Group 1, Period 3), K (Group 1, Period 4), and Ne (Group 18, Period 2).
3. Compare elements in the same group (Li, Na, K): ionization energy decreases as you move down the group because the outer electron is farther from the nucleus and more shielded by inner electrons.
4. Compare elements in the same period (Li and Ne): ionization energy increases from left to right due to increasing nuclear charge with the same shielding, making it harder to remove an electron.
5. Conclude that Ne (Neon), being a noble gas with a full valence shell and located at the far right of Period 2, has the highest ionization energy among the given elements.