After a chemical reaction,the total mass of reactants and products

Identify the law for which the following statement is true.
"Equal volume of all gases at same temperature and pressure should contain equal number of molecules".

Which of the following pairs of compounds illustrates the law of multiple proportions?

Pure samples of copper carbonate synthesized in the laboratory and found naturally both contain $51.35 \%$ copper,$38.91 \%$ carbon,and $9.74 \%$ oxygen by weight. This is in accordance with:

$n_1 \ g$ of substance $X$ reacts with $n_2 \ g$ of substance $Y$ to form $m_1 \ g$ of substance $R$ and $m_2 \ g$ of substance $S$. The reaction is represented as $X + Y \rightarrow R + S$. What is the relationship between the mass of the reactants and the mass of the products?

Which of the following examples illustrates the Law of Multiple Proportions?