The Data Booklet should be used for this question. The reaction shown is the most common ion-molecule reaction found in the gas clouds of the Universe. $\text{H}_2(\text{g}) + \text{H}_2^+(\text{g}) \rightarrow \text{H}(\text{g}) + \text{H}_3^+(\text{g})$. What might the composition of an $\text{H}_3^+$ ion be?
Chemistry 9701 · AS & A Level · Atoms, molecules and stoichiometry