Which of the following ions does not liberate hydrogen gas on reaction with dilute acids?

$\begin{array}{ll}\text{ ions }& \mathrm{E}°\left(\mathrm{V}\right)\\ {\mathrm{Ti}}^{2+}& -0.37\\ {\mathrm{V}}^{2+}& -0.26\\ {\mathrm{Cr}}^{2+}& -0.41\\ {\mathrm{Mn}}^{2+}& +1.57\end{array}$

A negative ${\mathrm{E}}^{\circ }$ value indicates that these metals release hydrogen from dilute acid.

$\left({\mathrm{M}}^2+2{\mathrm{H}}^{+}-\mathrm{e}\leftrightarrow {\mathrm{M}}^{3+}+{\mathrm{H}}_2\right)$

Therefore the correct option is A, ${\mathrm{Mn}}^{2+}$