Which of the following orders are correct with respect to their size? (1) \(\mathrm{Al}^{3+} \mathrm{I}^{-}…
Which of the following orders are correct with respect to their size?
(1) \(\mathrm{Al}^{3+} < \mathrm{Mg}^{2+} < \mathrm{Na}^{+} < \mathrm{F}^{-}\)
(2) \(\mathrm{Te}^{2-} > \mathrm{I}^{-} > \mathrm{Cs}^{+} > \mathrm{Ba}^{2+}\)
(3) \(\mathrm{Fe}^{3+} < \mathrm{Fe}^{2+} < \mathrm{Fe}^{4+}\)
(4) \(\mathrm{Mg} > \mathrm{Al} > \mathrm{Si} > \mathrm{P}\)
(1), (2) & (4)
(2), (3) & (4)
(1), (3) & (4)
(1), (2), (3) & (4)
Solution
(1) \(\mathrm{Mg}^{2+}, \mathrm{Na}^{+}, \mathrm{Al}^{3+}\) and \(\mathrm{F}^{-}\)are isoelectronic and thus follow the order \({ }_{13} \mathrm{Al}^{3+}<_{12} \mathrm{Mg}^{2+}<_{11} \mathrm{Na}^{+}<_{9} \mathrm{~F}^{-}\)
(2) Atomic number: \(\mathrm{Te}=52 ; \mathrm{I}=53 ; \mathrm{Cs}=55 ; \mathrm{Ba}=56\). All the ions given are isoelectronic and have the xenon electron configuration.
Ionic radius \(\propto \frac{1}{\text { nuclearcharge }}\)
Hence, the given order is correct.
(3) More the positive charge on the atom, less is the size.
The correct order would be
\(\mathrm{Fe}^{+2}<\mathrm{Fe}^{+3}<\mathrm{Fe}^{+4}\)
Option 3 is incorrect.
(4) Across the period, the size of atoms decreases. \(\mathrm{Mg}=160 \mathrm{pm} ; \mathrm{Al}=143 \mathrm{pm}\); \(\mathrm{Si}=118 ; \mathrm{P}=110 \mathrm{pm}\)
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