The lanthanide contraction refers to:

Options

A. radius of the series.
B. valence electrons of the series.
C. the density of the series.
D. electronegativity of the series.

Answer

A

Explanation

Due to 4f-orbial electrons (poor shielding effect),there is increase in effective nuclear charge which leads to the contraction of the size of atoms. This is called lanthanide contraction.