Question

If A, B, C, D are four different elements with outer electronic configuration as
A = $4s^2 4p^4$, B = $4s^2 4p^5$, C = $5s^2 5p^4$, D = $5s^2 5p^5$.
Find the element having highest ionization enthalpy ($\Delta_i H_1$)

• A. A
• B. B
• C. C
• D. D

Hint:

Trend: Across $\rightarrow$ Increase
Down $\rightarrow$ Decrease

Answer 1

The Correct Option is B

Concept: Ionization enthalpy:
• Increases across a period
• Decreases down a group
• Halogens ($p^5$) have higher values than chalcogens ($p^4$)

Step 1: Identify elements.
• A: Period 4, group 16
• B: Period 4, group 17
• C: Period 5, group 16
• D: Period 5, group 17

Step 2: Apply trends.
• Within same period: B > A
• Within same group: B > D (higher period → lower IE)

Step 3: Conclusion.
Highest ionization enthalpy = B Final Answer: Option (B)