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Question 600233
JEE Chemistry · Hard

Atomic Structure: Electron filling MCQ

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Electron fillingHardQuestion 600233

Question

The element with Z=24 (Cr) has configuration [Ar] 3d⁵ 4s¹ instead of [Ar] 3d⁴ 4s². This is because:
  1. A
    3d⁵ has a completely filled subshell
  2. B
    3d⁵ 4s¹ has extra stability due to half-filled 3d
    Correct
  3. C
    4s electron shielding decreases
  4. D
    The energy difference is negligible

Correct answer

3d⁵ 4s¹ has extra stability due to half-filled 3d

Explanation

Half-filled d subshell (3d⁵ = 5 unpaired electrons symmetrically arranged) has extra stability from exchange energy. This overcomes the normal Aufbau order.

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