Home › CBSE Class 9 › chemistry › atomicfoundations › Why do water samples from different sources (riv…
Why do water samples from different sources (river, rain, lab) all have the same hydrogen-to-oxygen mass ratio of approximately 1:8?
AAll water comes from rivers
BWater from different sources has different ratios
CThe law of constant proportions — the same compound (water = H₂O) always has the same composition by mass, regardless of source
DIt is a coincidence
Answer & Solution
Correct answer: C. The law of constant proportions — the same compound (water = H₂O) always has the same composition by mass, regardless of source
By the law of constant proportions, a given compound always has elements combined in the same ratio. Water is H₂O — 2 hydrogen atoms (each mass 1) + 1 oxygen atom (mass 16). Mass ratio H:O = 2:16 = 1:8. So 9 g of water always contains 1 g H + 8 g O — whether from the Ganga, Pacific Ocean, or distilled in a lab. This consistency is what makes 'water' a well-defined compound.