Assertion A: Copper (I) compounds are unstable in aqueous solution.

Reason R: Copper (I) compounds undergo dispropotionation to form$C{u}^{+2}\&Cu$  in aqueous solution

In an aqueous solution, many copper compounds become unstable and undergo a disproportionation reaction.
Cuprous ion (Cu⁺) is unstable in an aqueous medium because the stability of the aqueous medium depends on the energy of hydration.
In an aqueous solution, Cu⁺ is oxidised to produce stable form of Cu²⁺.

2Cu⁺→Cu+Cu²⁺