What term describes a high-molecular-weight synthetic organic compound that forms ions when dissolved in water?

The term that describes a high-molecular-weight synthetic organic compound that forms ions when dissolved in water is polymer. Polymers are large molecules made up of repeating structural units called monomers, which are covalently bonded. These compounds can dissolve in water and, depending on their chemical structure, they can dissociate and release ions into the solution, thus altering the characteristics of the water.

Polymers are commonly used in various applications, including water treatment processes, where their ability to form ions in solution can enhance flocculation, coagulation, and other removal processes for contaminants. Their high molecular weight contributes to their functionality in these chemical reactions and physical processes.

The other options refer to different concepts. A solvent is a substance that dissolves a solute to form a solution; emulsifiers help mix two immiscible liquids, like oil and water; and monomers are the smaller, individual units that combine to form polymers. Understanding these definitions helps in clarifying the unique role that polymers play in environmental science and water treatment.