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MHT CET202611 April 2026Evening ShiftChemistryd and f Block ElementsActual

Which transition series includes elements Co and Mo respectively?

Options

  1. A4d and 5d
  2. B5d and 6d
  3. C3d and 4d
  4. D3d and 6d

Correct answer

C. 3d and 4d

Step-by-step solution

Cobalt (Co) has the atomic number 27 and its electronic configuration is [ Ar ] 3d⁷ 4s² . It belongs to the first transition series, which is the 3d series. Molybdenum (Mo) has the atomic number 42 and its electronic configuration is [ Kr ] 4d⁵ 5s¹ . It belongs to the second transition series, which is the 4d series. Therefore, Co and Mo belong to the 3d and 4d transition series respectively. Answer: 3d and 4d

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