Which of the following elements belongs to the inner transition elements?

Which of the following statements is $INCORRECT$?

What does lanthanoid contraction result in?

Determine the correct $(T)$ and incorrect $(F)$ statements from the following:
$(a)$ Mischmetal contains lanthanoids and iron.
$(b)$ The symbol for Cerium is $Cs$.
$(c)$ The symbol for Cerium is $Ce$.

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

The number of $f$-electrons in the $+3$ oxidation state of gadolinium $(Z=64)$ is $x$ and in the $+2$ oxidation state of ytterbium $(Z=70)$ is $y$. The sum of $x$ and $y$ is: