  Question

Which of the following orders are correct with respect to their size?  (1) $$Al^{3+} < Mg^{2+} < Na^{+} < F^{-}$$                                    (2) $$Te^{2-} > I^{-} > Cs^{+} > Ba^{2+}$$ (3) $$Fe^{3+} < Fe^{2+} < Fe^{4+}$$ (4) $$Mg > Al > Si > P$$

A
(1),(2) & (4)  B
(2),(3) & (4)  C
(1),(3) & (4)  D
(1),(2),(3) & (4)  E
(2) & (4)  Solution

The correct option is A $$(1), (2)$$ & $$(4)$$(1) $$Mg^{2+}, Na^{+}, Al^{3+}$$ and $$F^-$$ are isoelectronic and thus follow the order $$_{13}Al^{3+} < _{12}Mg^{2+} < _{11}Na^{+} < _{9}F^{-}$$. (2) Atomic number : $$Te = 52; I = 53; Cs = 55; Ba = 56.$$ All the ions given are isoelectronic and have the xenon electron configuration. Ionic radius$$\propto \dfrac{1}{nuclear charge}$$Hence, the given order is correct.(3) More the positive charge on the atom, less is the size. The correct order would be $$Fe^{+2}<Fe^{+3}<Fe^{+4}$$Option 3 is incorrect.(4) Across the period, the size of atoms decreases. $$Mg = 160$$ pm; $$Al = 143$$ pm; $$Si = 118$$; $$P = 110$$ pm.Option A is the correct answer.Chemistry

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