Q1
The Law of Conservation of Mass states mass is:
Aneither created nor destroyed
Balways increasing
Calways decreasing
Dcreated during reactions
CBSEClass 9 (CBSE)ScienceCh 3 · Topic 1
Laws of Chemical Combination
Learning the fundamental laws governing chemical reactions and mass conservation.
Core concept
These two laws laid the foundation for modern chemistry and John Dalton's atomic theory, which proposed that matter is made of indivisible atoms that combine in fixed whole-number ratios to form compounds. For example, pure water always contains hydrogen and oxygen in the same 1:8 ratio by mass, whether the water comes from a river, rain, or is produced synthetically in a laboratory — this consistency is direct evidence supporting the Law of Constant Proportions.
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• Law of Conservation of Mass: mass is neither created nor destroyed in a chemical reaction.
• Law of Constant Proportions: a compound always has the same elements in the same fixed mass ratio.
• These laws led to Dalton's atomic theory of indivisible atoms combining in fixed ratios.
• Water always contains hydrogen and oxygen in a 1:8 mass ratio, regardless of its source.