The reason for chromium to have [Ar]3d⁵4s¹ configuration instead of [Ar]3d⁴4s² is

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Pauli's exclusion principle

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more exchange energy

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Detailed Solution

Electronic configuration of Cr is [Ar]3d⁵ 4s¹, instead of the expected [Ar]3d⁴ 4s². This is so because half filled d orbitals have extra stability.

The extra stability of half filled and completely filled configurations are due to,

(i) symmetry and (ii) exchange energy

In case of 3d⁵ configuration, no. of unpaired electrons(5) increases, exchange energy increases as a result stability increases.

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