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NEETChemistryClassification of Elements and Periodicity in Properties

How many exceptions to the classification of elements into blocks are there?

Options

  1. AOne exception
  2. BTwo exceptions
  3. CThree exceptions
  4. DFour exceptions

Correct answer

B. Two exceptions

Step-by-step solution

Helium belongs to the s-block but its positioning in the p-block along with other group 18 elements is justified because it has a completely filled valence shell (1s1) and as a result, exhibits properties characteristic of other noble gases. The other exception is hydrogen. It has only one s-electron and hence can be placed in group 1 (alkali metals). It can also gain an electron to achieve a noble gas arrangement and hence it can behave similar to a group 17 (halogen family) elements. Because it is a special case,

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