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ChemistryNEET 2025Modern periodic table and electronic basis

Classification of Elements and Periodicity in Properties

Which among the following electronic configurations belong to main-group elements?

A. [Ne]3s1\mathrm{[Ne]3s^1} · B. [Ar]3d34s2\mathrm{[Ar]3d^3 4s^2} · C. [Kr]4d105s25p5\mathrm{[Kr]4d^{10} 5s^2 5p^5} · D. [Ar]3d104s1\mathrm{[Ar]3d^{10} 4s^1} · E. [Rn]5f06d27s2\mathrm{[Rn]5f^0 6d^2 7s^2}

Choose the correct answer from the options given below:

  1. A.B and E only
  2. B.A and C only✓
  3. C.D and E only
  4. D.A, C and D only

Solution

Main-group elements have their outermost electrons in ss or pp orbitals: [Ne]3s1\mathrm{[Ne]3s^1} (Na) and [Kr]4d105s25p5\mathrm{[Kr]4d^{10}5s^25p^5} (I). B and D are dd-block, E is ff-block (a 6d6d actinoid configuration). So A and C.

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