Question

water’s chemical formula is \h₂o.\ what does this mean?
○ water is composed of hydrogen molecules and oxygen molecules.
○ a gram of water contains 20 hydrogen atoms.
○ water molecule contains two hydrogen atoms and one oxygen atom.
○ water molecules cannot be split into smaller pieces.

Explanation:

• Option 1: Water is made of H₂O molecules, not H₂ and O₂ molecules (that's for gaseous mixture), so wrong.
• Option 2: The formula shows atoms per molecule, not per gram, and "20" is incorrect, so wrong.
• Option 3: The subscript 2 on H and 1 (implied) on O in H₂O means each water molecule has 2 H atoms and 1 O atom, correct.
• Option 4: Water molecules can be split (e.g., via electrolysis) into H and O atoms, so wrong.

Answer:

A water molecule contains two hydrogen atoms and one oxygen atom.