Which series of elements are radioactive?

What is the general electronic configuration of actinoids?

Identify the ion having $4f^6$ electronic configuration.

Which element from the following has a half-filled $f$ orbital in the $+3$ oxidation state?

Which element from the following lanthanoids has a half-filled $f$-orbital in its observed and expected electronic configuration?

What are inner transition elements? Decide which of the following atomic numbers are the atomic numbers of the inner transition elements: $29, 59, 74, 95, 102, 104$.