The ease of adsorption of the hydrated alkali metal ions on an ion-exchange resin follows the order :
- Li+ < K+ < Na+ < Rb+
- Rb+ < K+ < Na+ < Li+
- K+ < Na+ < Rb+ < Li+
- Na+ < Li+ < K+ < Rb+
Answer
(2) Rb+ < K+ < Na+ < Li+
Solution
As per NCERT, smaller the cation, greater is its hydration. Li+ is the smallest ion, so it is the most hydrated:
Extent of hydration: Li+ > Na+ > K+ > Rb+
Size of hydrated ion: Li+ > Na+ > K+ > Rb+
The ease of adsorption of the hydrated ions on the resin increases with the extent of hydration,
Ease of adsorption: Rb+ < K+ < Na+ < Li+
Answer: (2)