Reason of lanthanoid contraction is:

Reason of lanthanoid contraction is:
  1. Negligible screening effect of 'f' orbitals
  2. Increasing nuclear charge
  3. Decreasing nuclear charge
  4. Decreasing screening effect

Solution

Lanthanoids are the f-block elements and 4f series element. The orbital size of the 4f is much bigger due to which electrons are spread in the large area, these electrons not able to shield charge from the nucleus. As a result, the poor screening effect or poor shielding effect of the 4f sub-shell. There is regular decrement of the atomic radius on increasing the atomic number.

Asked in: NEET 2014

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