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

• A. Oxygen (O)
• B. Helium (He)
• C. Neon (Ne)
• D. Fluorine (F)

Answer: (B)

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 due to increasing nuclear charge and decreases down a group due to increasing atomic radius and electron shielding.
3. Identify the positions of the given elements in the periodic table: Helium (He) and Neon (Ne) are noble gases in period 1 and 2 respectively; Oxygen (O) and Fluorine (F) are in period 2, with Fluorine to the right of Oxygen.
4. Recognize that noble gases have very high ionization energies because they have full valence shells, making it difficult to remove an electron.
5. Compare the elements based on their position: Helium is in period 1 and group 18, so it has the smallest atomic radius and highest effective nuclear charge among the options, leading to the highest first ionization energy.