What is the definition of a cation?

A cation is defined as an ion that carries a positive charge. This occurs when an atom loses one or more electrons, resulting in a net positive charge because the number of protons, which are positively charged, exceeds the number of electrons, which are negatively charged. Cations are important in various chemical reactions, as they can attract negatively charged ions, known as anions, to form ionic compounds.

The other options describe different states of ions or their structures. An ion with no charge would be a neutral atom, not classified as an ion at all. An ion that has a negative charge is referred to as an anion, not a cation. Lastly, an ion that contains multiple elements typically refers to polyatomic ions, which are also distinct from cations. Therefore, option D accurately defines a cation by highlighting its positive charge.