Total hardness of water is primarily a combination of which elements?

Total hardness of water is primarily considered to be the concentration of divalent metal ions, specifically calcium (Ca²⁺) and magnesium (Mg²⁺). These elements are predominantly responsible for the hardness found in water sources. When water comes into contact with soil and rocks, it often dissolves minerals, including calcium and magnesium, which enter the water supply.

Calcium is a common contributor to hardness as it is abundant in many geological formations, and magnesium often accompanies calcium in natural processes. The presence of both of these ions is what leads to the classification of water as hard or soft. Thus, when assessing total hardness, the focus is on both calcium and magnesium, making them the primary elements of concern in this context.

In contrast, the other options do not encompass the primary contributors to total hardness effectively. While calcium is certainly a major component, magnesium cannot be overlooked, as it is also essential in defining water hardness. Other combinations listed may include calcium, but without magnesium, they do not represent total hardness accurately. Together, calcium and magnesium create a comprehensive picture of water hardness, which is why the correct answer aligns with their pairing.