Question

Identify the correct order in which the ionic radius of the following ions increases:
(I) $F ^{-}$
(II) $Na ^{+}$
(III) $Na ^{3-}$

• A. III, I, II
• B. I, II, III
• C. II, III, I
• D. II, I, III

Answer 1

Answer: (D)

The species (atoms or ions) having the same number of electrons are known as isoelectronic species. In iso-electronic species, the size increases with the increase of negative charge and decrease of positive charge.
$\left(\right.$ size $\left.\propto \frac{1}{z / e\, \text{ratio}}\right) .$ i.e. effective nuclear charge.
Decreasing order of size.
$C ^{4-}> N ^{3-}> O ^{2-}> F ^{-}> Ne > Na ^{+}> Mg ^{2+}> Al ^{3+}> Si ^{4+}$