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

Answer: (B)

$Cs^+ > Rb^+ > K^+ > Na^+$

Answer 2

The smaller the size of the ion, the greater is the degree of hydration, thus degree of hydration is highest for $Li^+$ and lowest for $Cs^+$. Thus, $Li^+$ holds more water molecules in its hydration sphere and becomes largest in size among alkali metals and $Cs^+$ ion hold least number of water molecules. Hence, ionic mobility in highest for $Cs^+$ (due to its smallest size in aqueous solution) and lowest for $Li^+$ Thus, the order of ionic mobility in aqueous solution is $Cs^+ > Rb^+ > K^+ > Na^+$