Which definition best describes a cation?

A cation is defined as an atom that has lost one or more electrons, resulting in a net positive charge. When an atom loses electrons, it has more protons than electrons, leading to this positive charge. This property is fundamental to the behavior of cations in chemical reactions and bonding.

The other definitions do not accurately describe a cation. An atom with a negative charge refers to an anion, which is the opposite of a cation. An atom with an unpaired electron does not necessarily indicate a positive charge; it simply reflects its electron configuration, which may not be related to being a cation. Lastly, while a cation can be involved in covalent bonding, this definition is too broad and does not specifically address the electrical charge that defines a cation. Thus, the most accurate definition is that of an atom with a positive charge.