Determine the correct $(T)$ and incorrect $(F)$ statements from the following:
$(a)$ The symbol for Lanthanum is $La$.
$(b)$ The name of the element $Lu$ is Lanthanum.
$(c)$ The electronic configuration of $La^{3+}$ and $Ce^{4+}$ contains $4f^0$.

The only lanthanoid which is radioactive is:

Which is not the correct statement? (At. nos. $Ce = 58, Lu = 71, La = 57, Yb = 70$)

In lanthanides,with an increase in atomic number,the atomic radius decreases,except for the element $\underline{X}$. What is $\underline{X}$?

Describe the general chemical reactions of lanthanoids with the help of a diagram and state their uses.

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: