What is the common name for calcium sulfate?

Calcium sulfate, a chemical compound with the formula ( \text{CaSO}_4 ), is most commonly known as gypsum. Gypsum is a naturally occurring mineral that is often found in sedimentary environments, formed from the evaporation of seawater and can also be a byproduct of industrial processes. The common usage of the name "gypsum" for calcium sulfate is largely due to its historical and practical significance in construction and agriculture.

In construction, gypsum is a key ingredient in drywall and plaster, while in agriculture, it's used to improve soil structure and as a source of calcium and sulfur. The other options listed—lime, chalk, and soda ash—refer to different chemical compounds and thus do not align with the nomenclature for calcium sulfate. Lime typically refers to calcium oxide or calcium hydroxide, chalk is mainly composed of calcium carbonate, and soda ash is sodium carbonate. Each of these substances has distinct properties and uses, further clarifying why gypsum is the established common name for calcium sulfate.