Which of the following elements has the most favorable (most negative) electron affinity?

• A. Ne
• B. Cl
• C. O
• D. Na

Answer: (B)

Verified step by step guidance

1. Understand that electron affinity (EA) is the energy change when an atom gains an electron; a more negative value means the atom releases more energy and thus has a more favorable electron affinity.
2. Recall the general trend of electron affinity in the periodic table: it tends to become more negative across a period from left to right and less negative down a group.
3. Analyze each element: Neon (Ne) is a noble gas with a full valence shell, so it has a very low (less negative) electron affinity; Sodium (Na) is an alkali metal with a low electron affinity; Oxygen (O) is a nonmetal with a relatively high (more negative) electron affinity; Chlorine (Cl) is a halogen known for having one of the most negative electron affinities among the elements.
4. Compare the elements based on their group and period positions: Cl is in group 17 (halogens) and period 3, which typically have very favorable electron affinities due to their high electronegativity and desire to complete their valence shell.
5. Conclude that among the given options, Chlorine (Cl) has the most negative (most favorable) electron affinity because it releases the most energy when gaining an electron.