Which of the following orders of ionic radii is correctly...

Isoelectronic species refers to two atoms, ions or molecules that have the same electronic structure.

For isoelectronic species, ionic radii decrease with increase in nuclear charge (i.e., no. of protons). Thus, the cation with greater $+ ve$ charge will have a smaller radius and the anion with greater $- ve$ charge will have a larger radius.

${Na}^{+}, {F}^{-}, {O}^{- 2}, {Al}^{3 +}, {Mg}^{2 +}and{N}^{3 -}$ are isoelectronic. Hence, the order of their ionic radius is

${N}^{3 -} > {O}^{2 -} > {F}^{-} > {Na}^{+} > {Mg}^{2 +} > {Al}^{3 +}$.

For an atom, the cation is smaller than both neutral atom and anion.

Then correct size order for hydrogen, proton and hydride ion is

${H}^{-} > H > {H}^{+}$