How would you explain the lower atomic radius of $Ga$ as compared to $Al$?

Which of the following has the largest size?

$Na^{+}$,$Mg^{2+}$,$Al^{3+}$,and $Si^{4+}$ are isoelectronic. Their ionic size follows the order:

Given below are two statements:
Statement $I$: The metallic radius of $Na$ is $1.86 \ \mathring{A}$ and the ionic radius of $Na^{+}$ is lesser than $1.86 \ \mathring{A}$.
Statement $II$: Ions are always smaller in size than the corresponding elements.
In the light of the above statements,choose the correct answer from the options given below:

Arrange all elements of group $1$ in increasing order of their ionic radius.

From the given set of species,point out the species from each set having the least atomic/ionic radius:
$(A)$ $F^{-}, Na^{+}, Mg^{+2}$
$(B)$ $Ni, Cu, Zn$
$(C)$ $N^{-3}, Cs^{+}, H^{-}$
$(D)$ $Li, Li^{+}, Be^{+2}$