The ease of adsorption of the hydrated alkali metal ions om ion-exchange resins follows the order:

Options

A. `Li^(+)ltK^(+)ltNa^(+)ltRb^(+)`
B. `Rb^(+)ltK^(+)ltNa^(+)ltLi^(+)`
C. `K^(+)ltNa^(+)ltLi^(+)`
D. `Na^(+)ltLi^(+)ltK^(+)ltRb^(+)`

Answer

B

Explanation

the easeof adsorption of the hydreted alkali metal ion on an ion-exchange resist is directly related to the charge density of the hydrate ion. Since `Li^(+)` is very small, it is heavly hydrated. This makes the radius of the hydrated `Li^(+)` ion large and thus has very low chage density Consequenty, hydrated `Li^(+)` ions are attached less strongly to cation--exchange columns and hence eluted first.
In contrast, `Rb^(+)` , has relatively higher charge density. Consequently, hydrated `Rb^(+)` ions are attached more strongly to cation-exchange columns and hence eluted last. Thus, hte corrrect order is
`Rb^(+)ltK^(+)NaltLi^(+)`