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NEET Chemistry QUESTION #7399
Question 1
Which arrangement does NOT correctly represent the trend stated alongside 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
Ionisation enthalpy trend for B, C, N, O:
Generally IE₁ increases across a period. However, N has a half-filled 2p³ configuration (extra stability), so its IE₁ is higher than O.

Correct order: B < C < O < N (not B < C < N < O)

So option (2) is wrong. The I < Br < Cl < F order for EGE is also wrong (Cl > F), but option (3) is listed incorrectly too — however, the key answer is (2).