Ground water is particularly prone to excessive hardness due to the presence of:

ACalcium and sodium ions

BCalcium and magnesium ions ✓ Correct

CSodium and magnesium ions

DPotassium and calcium ions

Correct answer: (B) Calcium and magnesium ions

Explanation

Calcium and magnesium ions dissolved from rocks are the chief cause of hardness in ground water.

Sodium ions do not cause hardness and instead relate to salinity of water.

Combining sodium with magnesium still misplaces sodium as a hardness contributor.

Pairing potassium with calcium wrongly includes potassium, which does not harden water.

Hardness is measured as the total concentration of calcium and magnesium expressed as calcium carbonate.

Temporary hardness from bicarbonates can be removed by boiling, while sulphates cause permanent hardness.

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