SOLTUION : (a) In phosphorus chloride, $22.57$ gram of P combines with $77.43$ gram of chlorine.
(b) In phosphine, $91.18 g$ of $P$ combines with $8.82 g$ of hydrogen.
$\therefore 22.57 g$ of $P$ combines with $\frac{8.82}{91.18} \times 22.57=2.18 g$ of hydrogen
Hence the ratio between the weights of $Cl$ and $H$ which combine with a fixed wt. $(22.57 g )$ of $P$ is
$77.43: 2.18$ or $35.5: 1$.
(c) In $HCl$, the ratio between the weights of $Cl$ and $H$ is $97.23: 2.77$ or $35.5: 1$.
Since the two ratios between the weights of $Cl$ and $H$ are the same, the law of reciprocal proportions is proved.