$A$ 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?

"Mass can neither be created nor destroyed" is the statement of

When two elements combine to form more than one compound,the masses of one element that combine with a fixed mass of the other element are in a simple whole number ratio.
$(a)$ Is the statement given above correct?
$(b)$ If 'yes',which law does it follow?
$(c)$ Give an example corresponding to this law.

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?

Explain Dalton's atomic theory.

$n \ g$ of substance $X$ reacts with $m \ g$ of substance $Y$ to form $p \ g$ of substance $R$ and $q \ g$ of substance $S$. This reaction can be represented as,$X + Y \rightarrow R + S$. The relation which can be established in the amounts of the reactants and the products will be