Which of the following factors may be regarded as the main cause of lanthanide contraction ?

Options

A. Poor shielding of one of 4f electron by another in the subshell
B. Effective shielding of one of 4f electrons by another in the subshell
C. Poorer shielding of d 5d electrons by 4f electrons
D. Greater shielding of 5d electron by 4f electrons

Answer

C

Explanation

The shielding capability of 4f electrons is very poor. So 4f electrons cannot shield 5d electrons from the increasing nuclear charge as we move left to right in 4f – series of lanthanides.