When the volume is expressed,what does the law of definite proportions represent?

Different proportions of oxygen in the various oxides of nitrogen prove the

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".

Zinc sulfate crystals contain $22.65\%$ of zinc and $43.9\%$ of water. If it follows the law of definite proportions,how many grams of $Zn$ are required to obtain $20 \, g$ of crystals?

According to Dalton’s atomic theory,an atom

$A$ pure sample of water contains $88.89\%$ of oxygen by mass and $11.11\%$ of hydrogen by mass. This is an example of which law?