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NEETChemistryClassification of Elements and Periodicity in Properties

Assertion (A) The first ionisation energy of Be is greater than that of B . Reason (R) 2 p orbital has lower energy than 2 s orbital.

Options

  1. ABoth A and R are true and R is a correct explanation for A .
  2. BBoth A and R are true but R is not a correct explanation for A .
  3. CA is true but R is false.
  4. DA is false but R is true.

Correct answer

C. A is true but R is false.

Step-by-step solution

The first IE of Be is greater than that of B because Be has stable complete electronic configuration (1 s^2 2 s^2 ) , which require more energy to remove the first electron from its valence shell, whereas, B has electronic configuration 1 s^2 2 s^2 3 s^1 which require lesser energy than that of Be. In atoms with more than one electron, 2 s -orbital is lower in energy than 2 p -orbital. So, A is true, but R is false.

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