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KVPY2018ChemistryClassification of Elements and Periodicity in Properties

The correct order of energy of 2   s -orbitals in H , L i , N a and K , is

Options

  1. AK < N a < L i < H
  2. BN a < L i < K < H
  3. CN a < K < H < L i
  4. DH < N a < L i < K

Correct answer

A. K < N a < L i < H

Step-by-step solution

As the atomic number increases, the energy of orbital decreases. This is because the atomic radii decreases (nuclear charge increases) with increase in atomic number. The atomic number of H , L i , N a   and K respectively, are 1 , 3 , 11 and 19   . Thus, the correct order of energy of 2   s -orbitals is K < N a < L i < H

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