Which element is included in water hardness alongside calcium and magnesium?

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

Answer: (B)

Water hardness comes from dissolved minerals that carry positive charges, especially those that can form calcium carbonate. Calcium and magnesium are the main contributors because they are abundant and carry a 2+ charge. Other multivalent metals present in the water can also raise the total hardness, because hardness is often reported as calcium carbonate equivalents. Iron fits this idea: as Fe2+ or Fe3+ it adds to the overall hardness of the water. Monovalent ions like sodium or potassium don’t increase hardness in the standard measurement, and zinc isn’t typically counted toward hardness. So iron is the element that would be included in water hardness alongside calcium and magnesium.