NH₄⁺, or ammonium, is a positively charged ion formed when ammonia (NH₃) accepts a proton (H⁺). It plays a crucial role in various biological and chemical processes, including the nitrogen cycle, where it serves as a key nutrient for plants. In aqueous solutions, NH₄⁺ can exist alongside its counterpart, NH₃. It is commonly found in fertilizers, helping to promote plant growth. Additionally, NH₄⁺ is important in wastewater treatment, where it is converted into less harmful substances through microbial processes.