Which of the following species is stable in aqueous solution?

The species is ${\mathrm{MnO}}_4^{2-}$ stable in aqueous medium.

The species ${\mathrm{Cr}}^{2+}$ is rapidly oxidized to${\mathrm{Cr}}^{3+}$ by atmospheric oxygen.

${\mathrm{MnO}}_4^{3-}$ and${\mathrm{Cu}}^{+}$ disproportionate in solution.