Question

Which one of the following sets of compounds correctly illustrate the law of reciprocal proportions.

• A. $P_2{O}_3,P{H}_3,H_{2}O$
• B. $P_2{O}_5,P{H}_3,H_{2}O$
• C. $N_2{O}_5,N{H}_3,H_{2}O$
• D. $N_{2}O,N{H}_3,H_{2}O$
• E. $N{O}_2,N{H}_3,H_{2}O$

Answer 1

The correct option is A $P_2{O}_3,P{H}_3,H_{2}O$

Law of Reciprocal proportions:-

When two different elements combine with the same mass of a $3^{rd}$ element, the ratio of masses in which they do so must be same or multiple of the mass ratio in which they combine with each other.

$A)$ $P_2{O}_3,PH,H_{2}O$

The ratio of phosphorous combining with oxygen in $P_2{O}_3$ is

$P:O=62:48=31:24$

The ratio of Phosphorous combining with hydrogen in $P{H}_3$ is

$P:H=31:3$

The ratio of hydrogen combining with oxygen in $H_{2}O$ is

$H:O=2:16=1:8$ $⟶1$

Now, the ratio of hydrogen & oxygen combining with $P$

$\Rightarrow 3:24=1:8$ $⟶2$

From $1$ & $2$, $1:8$ is same in both cases

$\therefore$ Law of reciprocal proportions is illustrated correctly.