What defines a cation?

A cation is defined as a positively charged ion, meaning it has lost one or more electrons, resulting in a net positive charge. This characteristic aligns perfectly with the given choice of a positively charged sodium atom (Na+), which is a classic example of a cation. Sodium, when it loses its outermost electron, becomes Na+, demonstrating the fundamental property of cations: their positive charge.

The other options provided do not meet the definition of a cation. A negatively charged chloride atom (Cl-) is actually an anion, as it has gained an electron. An uncharged atom in a solution refers to a neutral state, which does not involve any charge. A particle formed from the reaction of two electrolytes may lead to the formation of ions, but it is not specifically defining what a cation is. Thus, the choice referring to the positively charged sodium atom correctly identifies a cation while illustrating essential concepts about ionic charge and behavior in solutions.