Final answer:
A copper compound, likely in a specific oxidation state, such as copper chloride (CuCl2), forms a green aqueous solution when dissolved in water, which can change color if further reactions, such as complexation, occur.
Step-by-step explanation:
The question pertains to the color of an aqueous solution when specific compounds are dissolved in water. Copper compounds are often responsible for green-colored solutions, specifically when copper is in a particular oxidation state. For instance, CuSO4 starts as a blue solution but can turn into a different color with further reactions. When discussing the formation of complex ions, the addition of aqueous ammonia to the pale blue aqueous solution of hydrated Cu2+ ions from CuSO4 leads to the new complex ion [Cu(NH3)4(H2O)2]2+, displaying an intense blue-violet color. However, for a green solution, copper chloride (CuCl2), which has a 2-to-1 chlorine to copper ratio, could be the unspecified green compound mentioned in this context.