Question

The concentration of which element is used to define the salinity of water?

Short answer

Answer: Sodium chloride (NaCl).

Step-by-step solution

Brief background on salinity

Salinity is a measure of the amount of salts dissolved in water, usually expressed in grams of salt per kilogram of water (g/kg) or parts per thousand (ppt). It is an important parameter in understanding the chemical properties of water, which affects its suitability for different purposes such as agriculture, drinking water, or marine ecosystems.

Identifying the key element

The element whose concentration is most commonly used to define the salinity of water is sodium chloride (NaCl), which is also known as common salt. Sodium (Na) and Chloride (Cl) ions are the two primary constituents of salts dissolved in water, and their concentration determines the level of salinity.