Question

The mass ratio of elements in a molecule are given below. Which among the following is incorrect with respect to law of constant proportion?

• A. $N{H}_3$, H:N mass ratio = 3:14
• B. $H_{2}O$, O:H mass ratio = 8:1
• C. ${\mathrm{CO}}_2$, O:C mass ratio = 8:3
• D. CO, O:C mass ratio = 5:3

Answer 1

The correct option is D CO, O:C mass ratio = 5:3

The atomic mass of the given elements are as follows:
* Nitrogen = 14 u
* Hydrogen = 1 u
* Oxygen = 16 u
* Carbon = 12 u
So the mass ratios are:
$N{H}_3$ = (3H:N) = 3:14
$H_{2}O$ = (O:2H) = 16:2 = 8:1
${\mathrm{CO}}_2$ = (2O:C) = 32:12 = 8:3
CO = (O:C) = 16:12 = 4:3
Hence, the mass ratio of O:C in CO i.e. 5:3 is incorrect.