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NEET Chemistry QUESTION #7418
Question 1
In which of the following options does the arrangement NOT agree with the property variation indicated against it?
  • \(\text{Al}^{3+} < \text{Mg}^{2+} < \text{Na}^+ < \text{F}^-\) (increasing ionic size)
  • B < C < N < O (increasing first ionisation enthalpy)✔️
  • \(\text{I} < \text{Br} < \text{Cl} < \text{F}\) (increasing electron gain enthalpy)
  • Li < Na < K < Rb (increasing metallic radius)
Correct Answer Explanation
IE₁ trend in Period 2:
Generally increases left to right, but N (half-filled 2p³) has unexpectedly higher IE₁ than O (2p⁴, one electron paired → easier to remove). So:

Correct order: B < C < O < N (N before O is reversed)

The statement B < C < N < O suggests O has higher IE₁ than N — this is wrong. Option (2) is incorrect.