Hydroxide ions, represented as OH⁻, are negatively charged ions composed of one oxygen atom and one hydrogen atom. They play a crucial role in chemistry, particularly in acid-base reactions. When an acid dissolves in water, it can release hydrogen ions, while bases often release hydroxide ions, leading to a balance in pH levels. In aqueous solutions, the concentration of hydroxide ions determines the solution's alkalinity. A higher concentration of OH⁻ indicates a more basic solution, while a lower concentration suggests acidity. Hydroxide ions are essential in various applications, including water treatment, agriculture, and industrial processes.