Question

proof for law of constant proportion

Answer 1

http://m.mugup.in/CM/Class-9/Chemistry/Atmos-And-Molecules/Law-Of-Constant-Proportions

There is clear explanation in this given link

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.