Which among the following is an actinoid element?

Which element from the following has a completely filled $f$-orbital in both observed and expected electronic configurations?

Identify the correct statement from the following:

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: $5f$ electrons can participate in bonding to a far greater extent than $4f$ electrons.
Reason $R$: $5f$ orbitals are not as buried as $4f$ orbitals.
In the light of the above statements,choose the correct answer from the options given below:

The elements in which electrons are progressively filled in $4f$ orbital are called

Discuss the trends in oxidation states shown by actinoids.