Question

Lanthanoids contraction is caused due to:

• A. the same effective nuclear charge from $Ce$ to $Lu$
• B. the imperfect shielding of outer electrons by $4f$ electrons from the nuclear charge
• C. the appreciable shielding of outer electrons by $4f$-electrons from the nuclear charge
• D. the appreciable shielding of outer electrons by $5d$-electrons from the nuclear charge

Answer 1

The correct option is B the imperfect shielding of outer electrons by $4f$ electrons from the nuclear charge

The imperfect shielding of outer s orbital electrons by 4f electrons from the nuclear charge results in greater than expected decrease in ionic radii of the elements in the lanthanide series known as lanthanide contraction.