Final answer:
A hydrogen ion, H+, is essentially a proton and in an aqueous solution, it is better represented as a hydronium ion, H3O+, showing its association with water molecules.
Step-by-step explanation:
A hydrogen ion, H+, is often referred to as a proton because it is a hydrogen atom that has lost its lone electron. However, we do not find bare protons in an aqueous solution since they are typically attracted to water molecules, forming hydronium ions (H3O+). The representation of H3O+ is more accurate for how a hydrogen ion exists in water. While in many chemical reactions, H+ and H3O+ are treated equivalently, the latter shows our understanding that protons are associated with water molecules, and not free-floating.