Which of the following atoms has the greatest electron affinity?

• A. Cl
• B. Mg
• C. Na
• D. O

Answer: (A)

Verified step by step guidance

1. Understand that electron affinity is the energy change that occurs when an atom gains an electron, typically measured in kJ/mol. A more negative value indicates a greater tendency to accept an electron.
2. Recall the general trend of electron affinity in the periodic table: it tends to increase (become more negative) across a period from left to right and decrease down a group.
3. Identify the positions of the given atoms in the periodic table: Mg (group 2), Na (group 1), O (group 16), and Cl (group 17).
4. Compare their electron affinities based on their group and period positions. Halogens (group 17) like Cl usually have high electron affinities because they need only one electron to complete their valence shell.
5. Conclude that among the given atoms, Cl has the greatest electron affinity due to its position as a halogen with a nearly full valence shell, making it highly eager to gain an electron.