Which orbitals,$4f$ or $5f$,are more capable of participating in bond formation?

Describe the atomic and ionic radii of lanthanoids and explain lanthanoid contraction.

Assertion : Ionisation enthalpies of the early actinoids are lower than for early lanthanoids.
Reason : $5f$ electrons are more effectively shielded from nuclear charge than $4f$ electrons.

The separation of $Lanthanoid$ elements is based on which of the following?

Which of the following is not a consequence of the Lanthanoid contraction?

Fill in the blanks given below:
$(i)$ Neptunium and Plutonium are obtained from ............ .
$(ii)$ Lanthanoid series and Actinoid series are known as ............ .
$(iii)$ The main energy level of an atom is called ............ .
$(iv)$ Elements that possess both metallic and non-metallic properties are called ............ .