Question
Which of the following factors may be regarded as the main cause of lanthanide contraction?
A.
Greater shielding of $$5d\,$$ electrons by $$4f$$ electrons
B.
Poorer shielding of $$5d\,$$ electrons by $$4f$$ electrons
C.
Effective shielding of one of $$4f$$ electrons by another in the subshell
D.
Poor shielding of one of $$4f$$ electron by another in the subshell
Answer :
Poor shielding of one of $$4f$$ electron by another in the subshell
Solution :
In lanthanides, there is poorer shielding of $$5d$$ electrons by $$4f$$ electrons resulting in greater attraction of the nucleus over $$5d$$ electrons and contraction of the atomic radii.