Q. The sequence of ionic mobility in aqueous solution is
A) Na⁺ > K⁺ > Rb⁺ > Cs⁺
B) K⁺ > Na⁺ > Rb⁺ > Cs⁺
C) Cs⁺ > Rb⁺ > K⁺ > Na⁺
D) Rb⁺ > K⁺ > Cs⁺ > Na⁺
Explanation
[Solution from source] Smaller ions have higher charge density and hold a larger shell of water molecules, so the hydrated Na⁺ ion is the bulkiest and moves slowest. Mobility therefore increases down the group: Cs⁺ > Rb⁺ > K⁺ > Na⁺. Na⁺ > ... > Cs⁺ follows bare ionic size and ignores hydration. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.