What is an ion?

An ion is defined as an atom or a molecule that has a net electric charge due to the loss or gain of one or more electrons. When an atom loses electrons, it acquires a positive charge and is referred to as a cation. Conversely, when an atom gains electrons, it becomes negatively charged and is known as an anion. This distinction is fundamental in chemistry, as ions play a crucial role in various chemical reactions, electrical conductivity in solutions, and the formation of ionic compounds.

In contrast to the other options, a molecule that cannot be decomposed refers to a stable and indivisible entity, not addressing the concept of charge. The term "compound" denotes a chemical substance made from two or more different elements chemically bonded together, which does not inherently imply the presence of a charge. Lastly, a homogeneous mixture describes a mixture with a uniform composition throughout, such as saltwater, which does not relate directly to the concept of ions or charge. Thus, the definition of an ion as an atom with a positive or negative charge is accurate and captures the essential characteristic that differentiates it from other chemical entities.