Question

Which of the following orders of ionic radii is correctly represented?

AIPMT 2014

Answer 1

$H$ has one electron and one proton, if one electron is added to the shell, the effective nuclear charge per electron decrease and electron cloud moves away from the nucleus hence radius increases.
On the other side, when the only electron of $H$ is removed sigle proton is left in atom having positive charge. There is no electron cloud as in to move away so ionic radius decreases as compared to $H^{-}$ and $H$.
So the order will be,
$H^{-}>H>H^{+}$

For isoelectronic species, the ionic radii is inversely proportional to their atomic number.

$\text{Ionic radii}\propto \frac{1}{\text{Atomic number}}$

Thus, option (b), (c) and (d) are incorrect.