Question

The sequence of ionic mobility in aqueous solution is

(a) Rb⁺ > K⁺ > Cs⁺ > Na⁺

(b) Na⁺ > K⁺ > Rb⁺ > Cs⁺

(c) K⁺ > Na⁺ > Rb⁺ > Cs⁺

(d) Cs⁺ > Rb⁺ > K⁺ > Na⁺

Answer 1

The correct option is: (d) Cs⁺ > Rb⁺ > K⁺ > Na⁺

Explanation:

Smaller the size of cation, higher will be the hydration and its effective size will increase and hence mobility in aqueous solution will decrease. Larger size ions have more ionic mobility due to less hydration. Thus the degree of hydration of M⁺ ions decreases from Li⁺ to Cs⁺. Consequently the radii of the hydrated ion decreases from Li⁺ to Cs⁺. Hence the ionic conductance of these hydrated ions increases from Li⁺ to Cs⁺ .