Answer
For a metal to be able to reduce an ion, that metal must be below it in Table 18.1. This means that the metal must be below Mn$^{2+}$ but above Mg$^{2+}$. Aluminum is the only metal in this table that meets this criteria.
Work Step by Step
For a metal to be able to reduce an ion, that metal must be below it in Table 18.1. This means that the metal must be below Mn$^{2+}$ but above Mg$^{2+}$. Aluminum is the only metal in this table that meets this criteria.
