Question

Which of the following is the correct order of radius?

• A. $\text{H}^{-}>\text{H}>\text{H}^{+}$
• B. $\text{N}\text{a}^{+}>\text{F}^{-}>\text{O}^{2 -}$
• C. $\text{F}^{-}>\text{O}^{2 -}>\text{N}\text{a}^{+}$
• D. $\text{A}\text{l}^{3 +}>\text{M}\text{g}^{2 +}>\text{N}^{3 -}$

Answer 1

Answer: (A)

For radius of atoms/ions
(i) For the same element:
$\text{r}\text{a}\text{d}\text{i}\text{u}\text{s} \, \text{o}\text{f} \, \text{a}\text{n}\text{i}\text{o}\text{n}>\text{a}\text{t}\text{o}\text{m}>\text{r}\text{a}\text{d}\text{i}\text{u}\text{s} \, \text{o}\text{f} \, \text{c}\text{a}\text{t}\text{i}\text{o}\text{n}$
(ii) For iso-electronic species:
$\text{r}\text{a}\text{d}\text{i}\text{u}\text{s} \propto \frac{1}{\text{a} \text{t} \text{o} \text{m} \text{i} \text{c} \, \text{n} \text{u} \text{m} \text{b} \text{e} \text{r}} \, $
Thus for option
$\left(\text{a}\right)$ correct order $ \rightarrow \text{H}^{-}> \, \text{H}>\text{H}^{+}$
$\left(\text{b}\right)$ correct order $ \rightarrow \text{O}^{2 -}>\text{F}^{-}>\text{N} \text{a}^{+}$
$\left(\text{c}\right)$ correct order $ \rightarrow \text{O}^{2 -}>\text{F}^{-}>\text{N} \text{a}^{+}$
$\left(\text{d}\right)$ correct order $ \rightarrow \text{N}^{3 -}>\text{M}\text{g}^{2 +}>\text{A}\text{l}^{3 +}$
Hence, $\text{H}^{-}>\text{H}>\text{H}^{+}$ is the correct option.