What does CaSO3 represent?

The formula CaSO3 represents calcium sulfite. In this compound, the calcium (Ca) carries a +2 charge, which is typical for alkaline earth metals. The sulfate group (SO3) consists of sulfur and oxygen, where sulfur is in the +4 oxidation state, combined with three oxygen atoms, leading to an overall -2 charge for the sulfite ion. Thus, when combining these two, calcium and sulfite, the formula naturally forms CaSO3.

Understanding the specific nomenclature here is crucial. "Sulfite" refers to the SO3^2- ion, distinguished from "sulfate," which would be represented by SO4^2-. This difference in the number of oxygen atoms is what makes the nomenclature specific, as they are commonly confused due to their similar naming conventions.

The other choices represent different compounds entirely. Calcium sulfate (the first option), for instance, would be represented as CaSO4, whereas calcium sulfide would be CaS, and calcium phosphate is a separate compound with a different formula that includes phosphate ions (PO4^3-). Each option thus highlights the importance of understanding the nuances in chemical nomenclature and formulas.