Identify an actinoid element from the following.

The most common oxidation state of Lanthanoid elements is $+3$. Which of the following is likely to deviate easily from $+3$ oxidation state?

The lanthanide ion having four unpaired electrons is
(Given : Atomic number of $Ce = 58, Nd = 60, Tb = 65$ and $Ho = 67$)

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:

Identify the correct actinide series from the following.

Identify the non-radioactive element from the following.