Question

Electron affinity is positive when:

• A. \( O \) changes into \( O^- \)
• B. \( O^- \) changes to \( O^{2-} \)
• C. \( O \) changes into \( O^+ \)
• D. \( O \) changes to \( O^{2+} \)

Hint:

The first electron affinity is typically exothermic because the atom stabilizes by gaining an electron. However, the second electron affinity is endothermic due to the repulsive forces between the negatively charged ion and the incoming electron.

Answer 1

The Correct Option is B

Step 1: {Understanding Electron Affinity}
Electron affinity is the energy alteration occurring when an electron is attached to a neutral gaseous atom, forming a negatively charged ion. The initial electron affinity typically releases energy (exothermic). Conversely, the second electron affinity usually requires energy input (endothermic). This energy requirement arises from the electrostatic repulsion experienced by the incoming electron due to the existing negative charge on the atom after the first electron's addition.
Step 2: {Explaining Positive Electron Affinity} 
For the oxygen ion \( O^- \), the inherent negative charge repels an incoming electron. This electrostatic repulsion necessitates energy input to overcome, resulting in a positive (endothermic) second electron affinity. Consequently, option (B) is the correct response.