Which two minerals contribute to scale?

The correct answer highlights the role of calcium and magnesium as key contributors to scale formation in various systems, particularly in industrial settings and water treatment processes.

Calcium and magnesium are both divalent cations that, when present in water, can react with carbonate ions and other anions to form insoluble salts. These insoluble salts precipitate out of the solution, leading to scale buildup in boilers, heat exchangers, and piping systems. This scale can significantly reduce efficiency and increase maintenance costs, making it essential to manage the concentrations of these minerals in systems where water is heated or pressurized.

The prevalence of calcium in natural water sources, along with magnesium primarily found in groundwater, makes their combination a significant concern for scale formation. They often coexist in a variety of water supplies, which underscores the importance of understanding their impact on scale development.

Other choices involve minerals that do not typically contribute to scale in the same way. Sodium, potassium, iron, and sulfur are less likely to form the types of hard deposits seen with calcium and magnesium, which is why they are not considered key players in scale formation. Focusing on calcium and magnesium allows for a clear understanding of how scale develops and the measures needed to prevent it.