Question

Which one of the following alkaline earth metal ions has the highest ionic mobility in its aqueous solution?

• A. $M{g}^{2+}$
• B. $S{r}^{2+}$
• C. $C{a}^{2+}$
• D. $B{e}^{2+}$

Answer 1

The correct option is B $S{r}^{2+}$

In aqueous solution, the ionic mobility is inversely proportional to the charge density on the ion.

• Charge per unit volume decreases down the group due to an increase in ionic radius.
• This reduces the attractive forces between water and the positive ion.
• This decreases the hydration radius and makes it easy for the ion to move.
• Thus, mobility increases down the group.

Hence $S{r}^{2+}$ has highest ionic mobility in water, among the given options.