Which of the following is not an actinide?

The correct order of atomic radii is

Choose the correct option regarding the following.
Assertion: Actinides exhibit a larger number of oxidation states than lanthanides.
Reason: There is a large energy gap between $5f$,$6d$ and $7s$ sub-shells.

Explain the lanthanoid contraction.

Larger number of oxidation states are exhibited by the actinoids than those by the lanthanoids,the main reason being

Describe the atomic and ionic radii of lanthanoids and explain lanthanoid contraction.