Question

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

• 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 electrons by 4f electrons

Answer 1

The correct option is A Poor shielding of one of 4f electron by another in the subshell

Lanthanoid contraction is due to poor sheilding effect of one of $4f$ electron by another in the subshell.