Question

Which of the following orders of ionic radii is correctly represented?

• A. $H^{-}>H^{+}>H$
• B. $N{a}^{+}>F^{-}>O^{2-}$
• C. $F^{-}>O^{2-}>N{a}^{+}$
• D. all are wrong

Answer 1

Answer: (D)

(No option is correct.)
(a) $H^{-}>H^{+}>H$
It is known that radius of a cation is always smaller than that of a neutral number of orbits. Whereas, the radius of anion is always greater than a cation due to decrease in effective nuclear charge. Hence, the correct order is
$H^{-}>H^{+}>H$
(b) $N{a}^{+}>F^{-}>O^{2-}$
The given species are isoelectronic as they contain same number of electrons. For isoelectronic species
Ionic radii $\propto \frac{1}{\text{atomic number}}$
Ion: $N{a}^{+}>F^{-}>O^{2-}$
Atomic number: 11 9 8
Hence, the correct order of ionic radii is
$O^{2-}>F^{-}>N{a}^{+}$
(c) Similarly, the correct option is
$O^{2-}>F^{-}>N{a}^{+}$
(d) Ions $A{l}^{3+}>M{g}^{2+}>N^{3-}$
Atomic number $13127$
Hence, the correct order is, $N^{3-}>M{g}^{2+}>A{l}^{3+}$