Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: Hydrogen gas and oxygen gas combine to form water. Which would be a more concise way of expressing what happens in this chemical reaction?
write a chemical equation
H2 + O2 → 2H2O.