Hardness in water is primarily due to which minerals?

• A. Sodium and potassium
• B. Calcium and magnesium
• C. Chloride and sulfate
• D. Nitrates

Answer: (B)

Hardness in water is driven by dissolved calcium and magnesium ions. These minerals come from rocks and soils and stay in solution, giving water its hard character. They also cause practical effects like forming scale on pipes and boilers and reacting with soaps to reduce lather. Sodium and potassium are present in water but don’t define hardness. Chloride, sulfate, and other ions affect salinity and taste, not the core hardness defined by calcium and magnesium. Nitrates are nutrients that indicate contamination and health concerns, not hardness. (Boiling can reduce carbonate-type hardness, which involves bicarbonates of calcium and magnesium, but sulfates and chlorides contribute to permanent hardness and are not removed by boiling.)