Which element from the following has the largest atomic size compared to the other three?

Which of the following is largest?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$:
Assertion $A$: The ionic radii of $O^{2-}$ and $Mg^{2+}$ are same.
Reason $R$: Both $O^{2-}$ and $Mg^{2+}$ are isoelectronic species.
In the light of the above statements,choose the correct answer from the options given below:

The ionic radius of $Na^{+}$ ions is $1.02 \ \mathring{A}$. The ionic radii (in $\mathring{A}$) of $Mg^{2+}$ and $Al^{3+}$,respectively,are

Which of the following represents the correct order of ionic radius?

Atomic radii of $Be, O, C, N, B$ are respectively (in $pm$):