The number of ions from the following that have the ability to liberate hydrogen from a dilute acid is _________.

$\mathrm{Ti}^{2+}, \mathrm{Cr}^{2+} \text { and } \mathrm{V}^{2+}$

<p>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.</p> <p>The standard reduction potentials for the ions mentioned are as follows:</p> <ul> <li>$\mathrm{Ti}^{2+}/\mathrm{Ti}$ is more negative than that of $\mathrm{H}^{+}/\mathrm{H}_{2}$.</li> <li>$\mathrm{Cr}^{2+}/\mathrm{Cr}$ also has a more negative standard reduction potential compared to $\mathrm{H}^{+}/\mathrm{H}_{2}$.</li> <li>The standard reduction potential for $\mathrm{V}^{2+}/\mathrm{V}$ is similarly more negative than that of $\mathrm{H}^{+}/\mathrm{H}_{2}$.</li> </ul> <p>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:</p> <p>Option C: 3</p>