Question

Which element among the Lanthanides has the smallest atomic radius?

• A. Cerium
• B. Lutetium
• C. Europium
• D. Gadolinium

Answer 1

The correct option is B Lutetium

The overall decrease in atomic and ionic radii from lanthanum to lutetium (the lanthanoid contraction) is a unique feature in the chemistry of the lanthanoids. This contraction is, of course, similar to that observed in an ordinary transition series and is attributed to the same cause, the imperfect shielding of one electron by another in the same sub-shell. However, the shielding of one 4 f electron by another is less than one d electron by another with the increase in nuclear charge along the series. There is fairly regular decrease in the sizes with increasing atomic number. The cumulative effect of the contraction of the lanthanoid series, known as lanthanoid contraction,

Lutetium is the last element of the Lanthanides, so it will have the smallest ionic radius due to Lanthanide contraction.