Question

Define law of constant proportion

Answer 1

 law of constant proportion
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It says that any pure compound always contain the same elements in definite proportion by weight irrespective of the method or source of preparation 

Answer 2

The law of constant proportions states that when a compound is broken, the masses of the constituent elements remain in the same proportion. Or, in a chemical compound, the elements are always present in definite proportions by mass.

This means each compound has the same elements in the same proportions, regardless of where the compound was obtained, who prepared it, or its mass.

This law was formulated and proven by Joseph Louis Proust in 1799.