Which of the following elements has the greatest ionization energy?

• A. K (potassium)
• B. Na (sodium)
• C. Ne (neon)
• D. Li (lithium)

Answer: (C)

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) on the periodic table and decreases down a group (top to bottom).
2. Identify the positions of the given elements on the periodic table: Li, Na, and K are all alkali metals in Group 1, with Li at the top, Na below it, and K further down. Ne is a noble gas in Group 18, at the end of the same period as Na.
3. Understand that noble gases like Ne have very stable electron configurations with full valence shells, which makes their ionization energies significantly higher than those of alkali metals.
4. Compare the ionization energies by considering both group and period trends: ionization energy increases from left to right across a period and decreases down a group, so Ne (far right in period 2) will have a higher ionization energy than Li, Na, or K.
5. Conclude that among the given elements, Ne has the greatest ionization energy due to its stable, full valence shell and its position on the periodic table.