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

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 $P_2 Q$.

Carbon and oxygen combine to form two oxides,carbon monoxide and carbon dioxide,in which the ratio of the weights of carbon and oxygen is respectively $12 : 16$ and $12 : 32$. These figures illustrate the:

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:

The following data are obtained when dinitrogen and dioxygen react together to form different compounds:

Mass of dinitrogen	Mass of dioxygen
$(i) \ 14 \ g$	$16 \ g$
$(ii) \ 14 \ g$	$32 \ g$
$(iii) \ 28 \ g$	$32 \ g$
$(iv) \ 28 \ g$	$80 \ g$

$(a)$ Which law of chemical combination is obeyed by the above experimental data? Give its statement.
$(b)$ Fill in the blanks in the following conversions:
$(i) \ 1 \ km = \dots \ mm = \dots \ pm$
$(ii) \ 1 \ mg = \dots \ kg = \dots \ ng$
$(iii) \ 1 \ mL = \dots \ L = \dots \ dm^{3}$

Under the same conditions of temperature and pressure,equal volumes of different gases contain an equal number of......