A hydroxide ion, represented as OH⁻, is a negatively charged ion made up of one oxygen atom and one hydrogen atom. It plays a crucial role in chemistry, particularly in acid-base reactions. Hydroxide ions are commonly found in bases, such as sodium hydroxide (NaOH), and contribute to the basicity of a solution. In water, hydroxide ions can form when water molecules dissociate. This process is essential for understanding pH levels, as solutions with higher concentrations of hydroxide ions are considered basic or alkaline. The presence of hydroxide ions is vital in various biological and industrial processes.