$Ce - 58$ is a member of

Which one of the following is a radioactive lanthanide?

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 $Ce$.

Which element from the following has a half-filled $4f$ orbital in its observed ground state?

In lanthanides,with an increase in atomic number,the atomic radius decreases,except for the element $\underline{X}$. What is $\underline{X}$?

In which of the following properties do $Lanthanoids$ and $Actinoids$ show similarity?