# What is a compound that produces hydrogen ions in solution?

$\text{An acid..............}$
In aqueous solution, any species that increases the concentration of the characteristic cation ${H}^{+}$ or ${H}_{3} {O}^{+}$ is called an acid. The actual acidium species is likely a cluster of water molecules with an EXTRA ${H}^{+}$, i.e. ${H}_{3} {O}^{+}$ or ${H}_{5} {O}_{2}^{+}$. It is convenient and chemically transparent to represent it is as ${H}^{+}$ or ${H}_{3} {O}^{+}$. The ${H}^{+}$ is conceived to be able to tunnel from cluster of water molecules to cluster.