Observe the following $f$-block elements: $Eu (Z=63)$; $Pu (Z=94)$; $Cf (Z=98)$; $Sm (Z=62)$; $Gd (Z=64)$; $Cm (Z=96)$. How many of the above have half-filled $f$-orbitals in their ground state?

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:

What does lanthanoid contraction result in?

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

Determine whether the following statements are True $(T)$ or False $(F)$:
$(a)$ All actinoid elements have a $7s^1$ configuration.
$(b)$ All actinoid elements have a $7s^0$ configuration.
$(c)$ There are no electrons in the $7s$ orbital of actinoids.

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$:
Assertion $A$: Size of $Bk^{3+}$ ion is less than $Np^{3+}$ ion.
Reason $R$: The above is a consequence of the lanthanoid contraction.
In the light of the above statements,choose the correct answer from the options given below: