Final answer:
The composition of water molecules can vary depending on their source, but if the water is pure, it will always consist of 88.8% oxygen by mass and 11.2% hydrogen by mass. This is because water molecules are composed of one oxygen atom and two hydrogen atoms, which have consistent atomic masses.
Step-by-step explanation:
Yes, the composition of water molecules can vary depending on their source. However, if the water is pure, it will always consist of 88.8% oxygen by mass and 11.2% hydrogen by mass, irrespective of its source or method of preparation.
This is because water molecules are composed of one oxygen atom and two hydrogen atoms, which have consistent atomic masses. Therefore, the relative proportions of oxygen and hydrogen in water will remain the same regardless of where the water comes from.