Which one of the following ions is the most stable in aqueous solution? (At. No. $\text{Ti}=22,\text{V}=23,\text{Cr}=24,\text{Mn}=25$)

In aqueous solution, stability depends on the hydration energy and the electronic configuration. ${\text{Cr}}^{3+}$ has a $d^3$ configuration ($t_{2g}^3$ in octahedral field). This half-filled $t_{2g}$ level provides extra stability due to high crystal field stabilization energy (CFSE). Thus, ${\text{Cr}}^{3+}$ is the most stable among the given ions in water.