Reason of lanthanoid contraction is

Options

A. negligible screening effect of f-orbitals
B. increasing nuclear change
C. decreasing nuclear charge
D. decreasing screening effect

Answer

A

Explanation

Lanthanoid contraction is the regular decrease in atomic and ionic radii of lanthanides. This is due to the imperfect shielding [or poor screening effect] of f-orbitals due to thieir diffused shape which unable to counterbalance the effect to the increased nuclear charge. Hence, the net results is a contraction in size of lanthanoids.