The set representing the correct order of ionic radius is :

As you move down a group in the periodic table, the number of electron shells increases, which naturally increases the ionic radius.

• Alkali Metals (Group 1): $$\text{Na}^+$$ sits below $$\text{Li}^+$$. Therefore, $$\text{Na}^+$$ has more electron shells than $$\text{Li}^+$$.
  $$\text{Na}^+ > \text{Li}^+$$
  
• Alkaline Earth Metals (Group 2): $$\text{Mg}^{2+}$$ sits below $$\text{Be}^{2+}$$. Therefore, $$\text{Mg}^{2+}$$ has more electron shells than $$\text{Be}^{2+}$$.
  $$\text{Mg}^{2+} > \text{Be}^{2+}$$

When species have the same number of electrons (isoelectronic) or are diagonally related, a higher positive charge pulls the remaining electrons closer to the nucleus, significantly shrinking the ionic radius.

• Comparing $$\text{Li}^+$$ and $$\text{Mg}^{2+}$$: While magnesium is a period below lithium, the $$+2$$ charge on $$\text{Mg}^{2+}$$ exerts a much stronger nuclear pull on its electrons than the $$+1$$ charge on $$\text{Li}^+$$. This extra positive charge shrinks $$\text{Mg}^{2+}$$ so much that it becomes smaller than $$\text{Li}^+$$.

  Hence,
  $$\text{Li}^+ > \text{Mg}^{2+}$$

Therefore, Overall can be written as 
$$\text{Na}^+ > \text{Li}^+ > \text{Mg}^{2+} > \text{Be}^{2+}$$