Question

A gaseous mixture contains $O_2$ and $N_2$ in the ratio of 1:4 by weight. The ratio of their number of molecules is:

• A. 1:4
• B. 1:8
• C. 7:32
• D. 3:16

Answer 1

The correct option is C 7:32

As given, the ratio of moles of $O_2:N_2=\frac{1}{32}:\frac{4}{28}=\frac{1}{32}:\frac{1}{7}$
(As we know, $mole=\frac{w}{M}$; molar mass of $O_2$ = 32 g/mol, molar mass of $N_2$ = 28 g/mol)
The ratio of number of molecules $=\frac{N_A}{32}:\frac{N_A}{7}=\frac{7}{32}:1=7:32$