Which of the following is a binary ionic compound?

A binary ionic compound consists of two elements: one metal and one nonmetal that are combined in a fixed ratio. In this case, potassium oxide is represented by K2O. Potassium (K) is a metal, and oxygen (O) is a nonmetal. The compound forms between these two elements through ionic bonds, where potassium donates electrons to oxygen, resulting in a compound with distinct ions (K⁺ and O²⁻).

Looking at the other choices, SiO2 is a covalent compound formed of silicon and oxygen, which are both nonmetals. P2O3 consists of two nonmetals (phosphorus and oxygen) and also does not fit the criteria of a binary ionic compound. CuSO3 features copper, a metal, but the sulfate ion (SO3²⁻) is a polyatomic ion, thus making it a complex ionic compound rather than a binary ionic compound.