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MHT CET202519 Apr 2025Evening ShiftChemistryd and f Block ElementsActual

Which transition series includes elements Co and Mo respectively?

Options

  1. A4 d and 5 d
  2. B5 d and 6 d
  3. C3 d and 4 d
  4. D3 d and 6 d

Correct answer

C. 3 d and 4 d

Step-by-step solution

The transition series classification depends on which d-orbital is being filled in the electronic configuration. For cobalt (atomic number 27) with configuration [ Ar ] 3d^7 4s^2 , the 3d subshell is incomplete, placing it in the 3d transition series. Molybdenum (atomic number 42) exhibits the exceptional configuration [ Kr ] 4d^5 5s^1 , where the 4d subshell is being filled, indicating membership in the 4d transition series. These assignments correspond to option C: 3d and 4d series.

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