Question

Which of the following is an endothermic process? \((g=\text{gas})\)

• A. \(\mathrm{Xe(g)+e^- \rightarrow Xe^-(g)}\)
• B. \(\mathrm{O(g)+e^- \rightarrow O^-(g)}\)
• C. \(\mathrm{Cl(g)+e^- \rightarrow Cl^-(g)}\)
• D. \(\mathrm{I(g)+e^- \rightarrow I^-(g)}\)

Hint:

Electron gain is generally exothermic for non-metals. \[ \boxed{\text{Noble gases have positive electron affinity (endothermic).}} \]

Answer 1

The Correct Option is A

Step 1: Recall the concept of electron affinity. The process \[ X(g)+e^-\rightarrow X^-(g) \] is generally exothermic for non-metals because energy is released when an electron is added.

Step 2: Identify the exceptional case. Noble gases have completely filled electronic configurations. Adding an electron to xenon requires energy, so the process is endothermic. Hence, \[ \mathrm{Xe(g)+e^-\rightarrow Xe^-(g)} \] is an endothermic process.

Step 3: Write the answer. Hence, \[ \boxed{\mathrm{Xe(g)+e^-\rightarrow Xe^-(g)}}. \] Thus, \[ \boxed{(A)} \] is the correct answer.