Question

Atomic radii of alkali metals (M) follow the order $Li<Na<K<Rb$ but ionic radii in aqueous solutions follow the reverse order $L{i}^{+}>N{a}^{+}>K^{+}>R{b}^{+}$.

The reason for the reverse order is :

• A. increase in the ionisation energy
• B. decrease in the metallic bond character
• C. increase in the electropositive character
• D. decrease in the amount of hydration

Answer 1

Answer: (D)

decrease in the amount of hydration

Atomic radil of alkali metals (M) follow the order $Li<Na<K<Rb$ but ionic radil in aqueous solutions follow the reverse order $L{i}^{+}>N{a}^{+}>K^{+}>R{b}^{+}$.

The reason of the reverse order is decrease in the amount of hydration.

Atomic/ionic radii increases from Li to Fr due to presence of an extra shell of electrons. In aqueous solution, ions are hydrated The degree of hydration is inversely proportional to the size of the ion.

Thus, Li ion being smallest in size (charge density more) is hydrated to maximum extent. Hence, it has maximum hydrated radius.

Therefore, the correct option is D.