Alkalinity in water is primarily due to carbonates, bicarbonates, and hydroxide ions.

• A. Acidity
• B. Turbidity
• C. Alkalinity
• D. Hardness

Answer: (C)

Water’s ability to resist changes in pH, its buffering capacity, comes mainly from carbonate species: carbonates, bicarbonates, and hydroxide ions. These ions act as buffers, neutralizing added acids and helping keep pH within a stable range. That buffering capacity is what alkalinity measures, so the statement is describing the correct concept.

The other ideas don’t capture this buffering role: acidity refers to proton-donating tendency and is not about buffering; turbidity is about cloudiness from suspended particles; hardness relates to dissolved calcium and magnesium minerals and is a different water quality attribute.