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".

The law of multiple proportions is illustrated by the two compounds:

To check the principle of multiple proportions,a series of pure binary compounds $(P_m Q_n)$ were analyzed and their composition is tabulated below. The correct option$(s)$ is(are)

Compound	Weight $\%$ of $P$	Weight $\%$ of $Q$
$1$	$50$	$50$
$2$	$44.4$	$55.6$
$3$	$40$	$60$

$(A)$ If empirical formula of compound $3$ is $P_3 Q_4$,then the empirical formula of compound $2$ is $P_3 Q_5$.
$(B)$ If empirical formula of compound $3$ is $P_3 Q_2$ and atomic weight of element $P$ is $20$,then the atomic weight of $Q$ is $45$.
$(C)$ If empirical formula of compound $2$ is $PQ$,then the empirical formula of the compound $1$ is $P_5 Q_4$.
$(D)$ If atomic weight of $P$ and $Q$ are $70$ and $35$,respectively,then the empirical formula of compound $1$ is $P_2 Q$.

One part of an element $A$ combines with two parts of another element $B$. Six parts of the element $C$ combine with four parts of the element $B$. If $A$ and $C$ combine together,the ratio of their weights will be governed by

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?

$A$ sample of calcium carbonate $(CaCO_3)$ has the following percentage composition: $Ca = 40\%$,$C = 12\%$,$O = 48\%$. If the Law of Definite Proportions is true,what is the weight of calcium in a $4 \ g$ sample of calcium carbonate?