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 $\to {\text{H}}^{-}>\text{H}>{\text{H}}^{+}$
$\left(\text{b}\right)$ correct order $\to {\text{O}}^{2-}>{\text{F}}^{-}>\text{N}{\text{a}}^{+}$
$\left(\text{c}\right)$ correct order $\to {\text{O}}^{2-}>{\text{F}}^{-}>\text{N}{\text{a}}^{+}$
$\left(\text{d}\right)$ correct order $\to {\text{N}}^{3-}>\text{M}{\text{g}}^{2+}>\text{A}{\text{l}}^{3+}$
Hence, ${\text{H}}^{-}>\text{H}>{\text{H}}^{+}$ is the correct option.