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NEET Chemistry QUESTION #7424
Question 1
For second period elements, the correct increasing order of first ionisation enthalpy is:
  • \(\text{Li} < \text{Be} < \text{B} < \text{C} < \text{N} < \text{O} < \text{F} < \text{Ne}\)
  • \(\text{Li} < \text{B} < \text{Be} < \text{C} < \text{O} < \text{N} < \text{F} < \text{Ne}\)
  • \(\text{Li} < \text{B} < \text{Be} < \text{C} < \text{N} < \text{O} < \text{F} < \text{Ne}\)
  • \(\text{Li} < \text{Be} < \text{B} < \text{C} < \text{O} < \text{N} < \text{F} < \text{Ne}\)✔️
Correct Answer Explanation
IE₁ anomalies in Period 2:
  • B < Be: Be (2s², full subshell) has higher IE₁ than B (2p¹, easier to remove)
  • O < N: N (2p³, half-filled, extra stable) has higher IE₁ than O (2p⁴, one paired electron easier to remove)
Correct order: Li < B < Be < C < O < N < F < Ne

Option (4) captures exactly these two inversions: Be before B is wrong; N before O is correct. Answer = option (2) per key. Li < B < Be < C < O < N < F < Ne.