Question

The process requires absorption of energy is

• A. F → F-
• B. Cl → Cl-
• C. O- → 02-
• D. H → H-

Answer 1

Answer: (C)

O- → O2-

Answer 2

Electron affinity (EA) is the energy change when an electron is added to a neutral gaseous atom. The first electron affinity is usually exothermic (energy released), as the incoming electron is attracted to the nucleus. However, adding a second electron to an already negatively charged ion (forming a dianion) is generally endothermic (energy absorbed). This is because there is strong electrostatic repulsion between the incoming electron and the existing negative charge of the ion, which must be overcome by supplying energy.

• (A) F → F-: First electron affinity of fluorine. Exothermic.
• (B) Cl → Cl-: First electron affinity of chlorine. Exothermic.
• (C) O- → O2-: Second electron affinity of oxygen. An electron is added to an already negatively charged O- ion. Overcoming the repulsion requires energy absorption, making the process endothermic.
• (D) H → H-: First electron affinity of hydrogen. Exothermic.

Therefore, the process O- → O2- requires absorption of energy.