Water hardness is a measure of dissolved minerals including calcium, magnesium, iron, and which other element?

• A. Strontium
• B. Potassium
• C. Sodium
• D. Zinc

Answer: (A)

Hardness reflects the presence of dissolved mineral ions, especially multivalent cations that form insoluble compounds with carbonate and sulfate. Calcium and magnesium are the primary contributors, but other similar metals can also raise hardness. Strontium sits in the same chemical family as calcium and magnesium, so when it’s dissolved in water it contributes to the overall mineral content that hardness measures. That’s why strontium is listed as the other element alongside calcium, magnesium, and iron in this context. Potassium and sodium are monovalent ions and don’t increase hardness in the same way, and zinc isn’t a typical hardness contributor in natural waters.