Which one of the following set of compounds correctly illustrates the law of reciprocal proportions?

The element $\mathrm{O} \mathrm{and} \mathrm{H}$ combine separately with the third element $\mathrm{P}$ to form ${\mathrm{P}}_2{\mathrm{O}}_3$ and ${\mathrm{PH}}_3$ respectively and directly combine to form ${\mathrm{H}}_2\mathrm{O}$. In ${\mathrm{PH}}_3$, $31$ parts by mass of $\mathrm{P}$ combine with $3$ parts by mass of $\mathrm{H}$ and in ${\mathrm{P}}_2{\mathrm{O}}_3$, $62$  parts by mass of $\mathrm{P}$ combine with $48$ parts by mass of $\mathrm{O}$. Thus the masses of $\mathrm{H} \mathrm{and} \mathrm{O}$ which combines with fixed mass of $\mathrm{H}$(say $62$ parts by mass) are $6 \mathrm{and} 48$ and they bear the ratio of $1:8$

Now in ${\mathrm{H}}_2\mathrm{O}$, $2$ parts by mass of $\mathrm{H}$ combines with $16$ parts by mass of $\mathrm{O}$. So, they combine in ratio $2:16$ which is equal to $1:8$ which is same as the first ratio.