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

• A
  $Li^{+} < K^{+} < Na^{+} < Rb^{+}$
• B
  $Rb^{+} < K^{+} < Na^{+} < Li^{+}$
• C
  $K^{+} < Na^{+} < Rb^{+} < Li^{+}$
• D
  $Na^{+} < Li^{+} < K^{+} < Rb^{+}$