Question

The sequence of ionic mobility in aqueous solution is

• A. $K^{+}>N{a}^{+}>R{b}^{+}>C{s}^{+}$
• B. $C{s}^{+}>R{b}^{+}>K^{+}>N{a}^{+}$
• C. $R{b}^{+}>K^{+}>C{s}^{+}>N{a}^{+}$
• D. $N{a}^{+}>K^{+}>R{b}^{+}>C{s}^{+}$

Answer 1

Answer: (B)

The smaller the size of the ion, the greater is the degree of hydration, thus degree of hydration is highest for $L{i}^{+}$ and lowest for $C{s}^{+}$. Thus, $L{i}^{+}$ holds more water molecules in its hydration sphere and becomes largest in size among alkali metals and $C{s}^{+}$ ion hold least number of water molecules. Hence, ionic mobility in highest for $C{s}^{+}$ (due to its smallest size in aqueous solution) and lowest for $L{i}^{+}$ Thus, the order of ionic mobility in aqueous solution is
$C{s}^{+}>R{b}^{+}>K^{+}>N{a}^{+}$