In the lanthanide series,the element well known to exhibit $+4$ oxidation state is

$Ce - 58$ is a member of

Which is the general formula for the electronic configuration of the actinide series?

Which of the following elements shows the maximum number of different oxidation states in its compounds?

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:

Which actinoid from the following has the smallest ionic size in the $+3$ oxidation state?