Question

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

• A. $H^- > H^+ > H$
• B. $Na^+ > F^- > O^{2-}$
• C. $F^- > O^{2-} > Na^{+}$
• 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) $Na^+ > F^- > O^{2-}$
The given species are isoelectronic as they contain same number of electrons. For isoelectronic species
Ionic radii $\propto \frac{1}{\text{atomic number}}$
Ion: $Na^+ > F^- > O^{2-}$
Atomic number: 11 9 8
Hence, the correct order of ionic radii is
$O^{2-} > F^- > Na^+$
(c) Similarly, the correct option is
$O^{2-} > F^- > Na^+$
(d) Ions $Al^{3+} > Mg^{2+} > N^{3-}$
Atomic number $13 \, \, 12 \, \, \, 7$
Hence, the correct order is, $N^{3-} > Mg^{2+} > Al^{3+}$