Question

The sequence of ionic mobility in aqueous solution is :
(a) K⁺ > Na⁺ > Rb⁺ > Cs⁺ (b) Cs⁺ > Rb⁺ > K⁺ > Na⁺
(c) Rb⁺ > K⁺ > Cs⁺ > Na⁺ (d) Na⁺ > K⁺ > Rb⁺ > Cs⁺

Answer 1

Explanation:

The sequence of ionic mobility in aqueous solution is (c) Rb⁺ > K⁺ > Cs⁺ > Na⁺

Answer 2

The sequence of ionic mobility in aqueous solution is :  

(b) Cs⁺ > Rb⁺ > K⁺ > Na⁺

Ionic mobility is dependent on the atomic size of the alkali metal in its aqeous solution. Ionic mobility decreases with increase in atomic size.

As the size of the cation decreases, the hydration will increase, due to which the effective size will increase and conversely, the mobility will decrease.

For the opposite case, ions with large size have less hydration, as a result, the  ionic mobility for them increases.

Again, in a group of a periodic table, as we go down a group, atomic size increases.

So, Cs has the maximum size followed by Rb, K and then Na.

Similarly, ionic mobility in aqeous solution also varies like:

Cs⁺ > Rb⁺ > K⁺ > Na⁺

Thus, option (b) is correct.