Which of the following elements is most likely to have an electron affinity value closest to zero?

• A. Na
• B. Al
• C. Ar
• D. Rb

Answer: (C)

Verified step by step guidance

1. Understand that electron affinity (EA) is the energy change when an atom gains an electron. Elements with high EA values release more energy when gaining an electron, while those with EA close to zero do not gain electrons easily.
2. Recall that noble gases like Argon (Ar) have a full valence shell, making them very stable and unlikely to gain electrons. This results in electron affinity values close to zero or even positive (indicating energy must be supplied to add an electron).
3. Compare the given elements: Sodium (Na) and Rubidium (Rb) are alkali metals with relatively low but negative electron affinities, meaning they release some energy when gaining an electron. Aluminum (Al) is a metal with a moderate electron affinity.
4. Since Argon (Ar) is a noble gas with a complete octet, it is the least likely to gain an electron, so its electron affinity is closest to zero compared to the other elements listed.
5. Therefore, the element with an electron affinity value closest to zero among the options is Argon (Ar).