To determine the ability of the ions to liberate hydrogen from a dilute acid, we need to understand the standard electrode potentials of these ions in comparison to hydrogen. The standard electrode potential of hydrogen ($$\mathrm{H}^{+}/\mathrm{H}_{2}$$) is set at 0 volts. Any metal ion with a negative standard reduction potential compared to hydrogen has the ability to liberate hydrogen gas from dilute acids because they are more likely to donate electrons to the $$\mathrm{H}^{+}$$ ions found in acids, reducing them to $$\mathrm{H}_{2}$$ gas.

The standard reduction potentials for the ions mentioned are as follows:

• $$\mathrm{Ti}^{2+}/\mathrm{Ti}$$ is more negative than that of $$\mathrm{H}^{+}/\mathrm{H}_{2}$$.
• $$\mathrm{Cr}^{2+}/\mathrm{Cr}$$ also has a more negative standard reduction potential compared to $$\mathrm{H}^{+}/\mathrm{H}_{2}$$.
• The standard reduction potential for $$\mathrm{V}^{2+}/\mathrm{V}$$ is similarly more negative than that of $$\mathrm{H}^{+}/\mathrm{H}_{2}$$.

Due to their negative standard reduction potentials relative to hydrogen, all three ions ($$\mathrm{Ti}^{2+}, \mathrm{Cr}^{2+}, \mathrm{V}^{2+}$$) have the capacity to liberate hydrogen from a dilute acid. Therefore, the correct answer is:

Option C: 3