Which of the following is a common characteristic of an anion?

An anion is defined as an ion that carries a negative charge. This characteristic stems from the fact that anions are formed when atoms gain one or more electrons, resulting in an excess of negatively charged electrons compared to positively charged protons within the nucleus. Consequently, the accumulation of these extra electrons leads to a charge imbalance, manifesting as a negative charge.

Understanding this concept is crucial in various fields, including wastewater treatment, where the behavior of ions dictates the interactions and reactions that take place within treatment processes. For instance, anions play significant roles in the chemistry of wastewater, influencing factors such as pH levels, solubility of pollutants, and the effectiveness of treatment methods.

The other options highlight different characteristics that do not define anions. For example, positive charge refers specifically to cations, while neutrality indicates an uncharged atom or molecule. Reactivity with water is a trait that can apply to both cations and anions but does not specifically relate to the fundamental definition of an anion. Therefore, the identification of anions as possessing a negative charge is a foundational concept in understanding ionic behavior in wastewater management and other chemical contexts.