Final answer:
The chemical formula H₂O represents water, which is option 1) in the given choices. Water, regardless of being in liquid, ice, or steam form, maintains the same chemical formula.
Step-by-step explanation:
The substance represented by the chemical formula H₂O is water. Other substances mentioned such as carbon dioxide, methane, and ammonia have different chemical formulas. Carbon dioxide is represented by CO₂, methane by CH₄, and ammonia by NH₃. Water can be found in various states like liquid, ice, and steam, but regardless of its state, the chemical formula remains H₂O. Simple molecules often have common names in chemical nomenclature, and for H₂O, the common name is water, not dihydrogen monoxide. Therefore, the correct answer to the question is option 1) Water.