What is the chemical formula for hydronium?

Hydronium is the ion that forms when a water molecule (H2O) accepts an additional hydrogen ion (H+). This process occurs in aqueous solutions, particularly in acid-base reactions. The addition of the extra hydrogen ion to water results in the formation of the hydronium ion, which has the chemical formula H3O+.

In terms of its structure, the hydronium ion consists of three hydrogen atoms covalently bonded to one oxygen atom, making it a positively charged species due to the extra proton. This charge is essential for understanding its role in acid-base chemistry, where hydronium ions are often regarded as the predominant form of hydrogen ions in solution.

The other options represent different chemical species: H2O is water, OH- is the hydroxide ion, and H+ is a proton. However, H+ in aqueous solutions does not exist freely; it interacts with water to form H3O+, making the hydronium ion the correct representation of a hydrogen ion in solution.