Which one of the following species is stable in aqueous solution?

Step-by-step solution

In M n O 4 2 - , manganese is in + 6 oxidation state, which is having the highest stability. MnO 4 - 2 ⇒​ x + 4   - 2 = - 2 x = 6 Cu + ⇒ x = + 1 It will disproportionate in aqueous solution. Cr + 2 ⇒ x = + 2 It will also disproportionate in aqueous solution. MnO 4 - 3 ⇒ x + 4 - 2 = - 3 Mn is not stable in +5 oxidation state. x = 5 Higher the oxidation state, more is the stability of the species.