The correct option is (d) Cu+.
Explanation:
Copper (I) compounds are unstable in aqueous solution and undergo disproportio-nation.
2Cu+ ---> Cu2+ + Cu
The greater stability of Cu2+(aq) than Cu+(aq) is due to much more -ve Δhyd H of Cu2+(aq) than Cu+(aq) which is more than compensates for the second ionisation enthalpy of Cu.