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NEETChemistryClassification of Elements and Periodicity in Properties

Which of the following electronic configurations represents a d-block element belonging to the 5th period?

Options

  1. A[ Kr ] 4 d ^5 5 s ^1
  2. B[ Ar ] 3 d ¹⁰ 4 s ^2 4 p ^3
  3. C[ Xe ] 4 f ¹⁴ 5 d ^2 6 s ^2
  4. D[ Kr ] 5 s ^2

Correct answer

A. [ Kr ] 4 d ^5 5 s ^1

Step-by-step solution

The period of an element is given by the highest principal quantum number ( n ) of its valence shell. [ Kr ] 4 d ^5 5 s ^1 : The highest principal quantum number is n=5 , so it belongs to the 5th period. The last electron enters the 4 d subshell, making it a d-block element. This is the correct configuration. [ Ar ] 3 d ¹⁰ 4 s ^2 4 p ^3 : The highest principal quantum number is n=4 (4th period) and the last electron enters the 4 p subshell (p-block). [ Xe ] 4 f ¹⁴ 5 d ^2 6 s ^2 : The highest principal quantum numbe

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