Which of the following is a chemical characteristic of water?

The correct answer is hardness because it reflects the concentration of dissolved minerals, mainly calcium and magnesium, in the water. Hardness is considered a chemical characteristic because it results from the presence of these specific ions, affecting water quality and its behavior in different applications, such as its efficiency in soap and detergent usage and the potential for scaling in pipes and appliances.

In contrast, color is a physical characteristic that can indicate the presence of certain organic materials, metals, or other particulates, but it does not directly involve the chemical composition of the water itself. Bacteria represent biological characteristics rather than chemical ones, as they pertain to the presence of living organisms in the water. Temperature, while it can influence chemical reactions in water, is primarily a physical property that affects water's state and behavior rather than its chemical makeup.