What does lanthanoid contraction result in?

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

Which lanthanoid element exhibits $+2$ and $+3$ oxidation states?

Which of the following lanthanoids have $[Xe] 4f^x 5d^1 6s^2$ configuration in their ground state? $(x = 1-14)$

The element having electronic configuration $ns^2(n-1)d^{1-10}(n-2)f^{1-14}$ belongs to:

Given below are two statements:
Statement $I$: In the Lanthanoids,the formation of $Ce^{+4}$ is favoured by its noble gas configuration.
Statement $II$: $Ce^{+4}$ is a strong oxidant reverting to the common $+3$ state.
In the light of the above statements,choose the most appropriate answer from the options given below: