What do buffers do in natural water systems?

• A. Buffers resist pH changes by neutralizing added acids or bases
• B. Buffers raise pH when acids are added
• C. Buffers remove minerals
• D. Buffers increase temperature

Answer: (A)

In natural water, buffering means the water can resist changes in pH when acids or bases are added. This happens mainly through the carbonate–bicarbonate system. When acid is added, the extra hydrogen ions are taken up by bicarbonate and carbonate species (for example, bicarbonate can convert to carbonic acid, which becomes CO2 and water), so the pH doesn’t drop as much. When base is added, the system can supply H+ to form carbonic acid and bicarbonate, helping keep the pH from rising too quickly. This stabilizing effect is why natural waters have alkalinity, a measure of their buffering capacity. So the best description is that buffers resist pH changes by neutralizing added acids or bases.

The other statements aren’t the defining role: buffers don’t inherently raise pH when acids are added, they don’t remove minerals, and they don’t increase temperature.