question_answer

Which of the following factors may be regarded as the main cause of lanthanide contraction [AIEEE 2005]

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 \[5d\] electrons by \[4f\] electrons

D) Greater shielding of \[5d\] electron by \[4f\] electrons