Concept:The Law of Definite Proportions states that a given chemical compound always contains its component elements in fixed ratio (by mass), regardless of the compound's source.
Formula:$$ \% \text{ Element} = \left( \frac{\text{Mass of element in 1 mole}}{\text{Molar mass of compound}} \right) \times 100 $$
Solution:- The chemical formula for water is \( \text{H}_2\text{O} \).
- Molar mass of \( \text{H}_2\text{O} = (2 \times 1) + 16 = 18 \text{ g/mol} \).
- Mass of Hydrogen in 1 mole = 2g.
- \( \% \text{ Hydrogen} = (2 / 18) \times 100 = 11.11\% \).
- Mass of Oxygen in 1 mole = 16g.
- \( \% \text{ Oxygen} = (16 / 18) \times 100 = 88.89\% \).
Why other options are incorrect:- Option B, C, D: These are incorrect percentage ratios that contradict the fundamental 1:8 mass ratio (2g H to 16g O) inherent to water molecules.
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