What defines alkalinity in water?

Alkalinity in water is fundamentally defined by its ability to resist changes in pH when strong acids are added to it, which allows the water to effectively absorb hydrogen ions without a significant change in pH. This property is primarily due to the presence of bicarbonate (HCO3−) and carbonate (CO3^2−) ions, which act as buffers. These ions play a crucial role in maintaining stable pH levels, especially in natural water systems, and are vital in processes such as nutrient uptake by plants and the overall health of aquatic ecosystems.

The other concepts presented are not relevant to the definition of alkalinity. For instance, the presence of strong acids would typically decrease alkalinity rather than define it, while measuring metal content and dissolved oxygen focuses on different aspects of water quality and chemistry unrelated to alkalinity. Overall, Option B appropriately captures the essence of how alkalinity functions in water chemistry.