A) \[N<Be<B\]
B) \[{{F}^{-}}<{{O}^{2-}}<{{N}^{3-}}\]
C) \[Na<Li<K\]
D) \[F{{e}^{3+}}<F{{e}^{2+}}<F{{e}^{4+}}\]
Correct Answer: B
Solution :
These are isoelectronic species and their radii decreases with increasing their atomic number due to increasing effective nuclear charge \[({{Z}_{eff}}).\] \[{{Z}_{eff}}=Z-\sigma \]where, \[{{Z}_{eff}}=\] effective nuclear charge, Z = atomic number and \[\sigma =\] screening constant. For \[{{F}^{-}},{{O}^{2-}}\]and \[{{N}^{3-}},\] the value ofcis constant due to equal number of electrons. So order of \[{{Z}_{eff}}\] is \[{{F}^{-}}>{{O}^{2-}}>{{N}^{3-}}\] hence, order of radii \[={{F}^{-}}<{{O}^{2-}}<{{N}^{3-}}\left( radii\propto \frac{1}{{{Z}_{eff}}} \right).\]
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