Question

Which of the following set of compounds cannot illustrate law of reciprocal proportion?
(i)P2O3, PH3, H2O
(ii)P2O5, PH3, H2O
(iii)N2O5, NH3, H2O
(iv)N2O, NH3, NO2
​

Answer 1

Explanation:

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 PH

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

⇒3:24=1:8 ⟶2

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

∴ Law of reciprocal proportions is illustrated correctly.