H⁺, or hydrogen ion, is a positively charged ion formed when a hydrogen atom loses its electron. It plays a crucial role in various chemical reactions, particularly in acid-base chemistry. The concentration of H⁺ ions in a solution determines its acidity; higher concentrations indicate stronger acids. In biological systems, H⁺ ions are essential for processes like cellular respiration and photosynthesis. They are involved in the formation of ATP, the energy currency of cells, and help maintain the pH balance in organisms. Understanding H⁺ is vital for studying chemistry, biology, and environmental science.