Every water molecule has two hydrogen atoms bonded to one oxygen atom. this fact supports the concept that elements in a compound are
(1) chemically combined in a fixed proportion
(2) chemically combined in proportions that vary
(3) physically mixed in a fixed proportion
(4) physically mixed in proportions that vary

The answer is (1) chemically combined in a fixed proportion. Elements in a compound are bound by a chemical bond. So, oxygen and hydrogen are bound chemically. Further, their proportion never changes, it is always 1 oxygen atom and 2 hydrogen atoms in water. Thus, elements in a compound are chemically combined in a fixed proportion.Hope this helps. Let me know if you need additional help!

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