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MHT CET202616 April 2026Morning ShiftChemistryStructure of AtomActual

What is the observed electronic configuration of Cu ?

Options

  1. A[ Ar ] 3d^9 4s^2
  2. B[ Ar ] 3d¹⁰ 4s^1
  3. C[ Ar ] 3d^5 4s^2
  4. D[ Ar ] 3d^6 4s^2

Correct answer

B. [ Ar ] 3d¹⁰ 4s^1

Step-by-step solution

The atomic number of copper (Cu) is 29 . According to the Aufbau principle, the expected electronic configuration is [ Ar ] 3d^9 4s^2 . However, a completely filled d -subshell ( 3d¹⁰ ) provides extra stability due to symmetrical electron distribution and higher exchange energy. Therefore, one electron from the 4s orbital is transferred to the 3d orbital, resulting in the observed electronic configuration of [ Ar ] 3d¹⁰ 4s^1 . Answer: [ Ar ] 3d¹⁰ 4s^1

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