Which process allows some minerals to dissolve in water in a river system?

The correct process that allows some minerals to dissolve in water in a river system is solution. This process occurs when water, often in rivers, comes into contact with certain minerals, causing the minerals to dissolve and become part of the water's chemical composition. This is especially common with minerals such as limestone or salts, which readily dissolve in water.

In contrast, traction involves heavy particles being dragged along the riverbed, while saltation refers to the bouncing motion of smaller particles as they are propelled forward by the water's force. Suspension describes the process by which tiny particles remain floating in the water, but these processes do not involve the actual dissolution of minerals. Solution is distinct because it specifically describes the chemical process of dissolution, making it the correct answer for identifying how minerals become part of the water in a river.