Question

is the law of constant composition is true for all types of compounds explain why or why not?

Answer 1

In chemistry, the law of definite proportions, sometimes called Proust's Law,
states that a chemical compound always contains exactly the same proportion of
elements by mass. An equivalent statement is the law of constant composition,
which states that all samples of a given chemical compound have the same
elemental composition by mass. For example, oxygen makes up about 8/9 of the
mass of any sample of pure water, while hydrogen makes up the remaining 1/9 of
the mass. Along with the law of multiple proportions, the law of definite
proportions forms the basis of stoichiometry.