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

Weight ratio of ${\text{O}}_2:{\text{N}}_{\text{2}}=1:4$

${\text{No.of\hspace{0.17em}moles\hspace{0.17em}of\hspace{0.17em}O}}_2=\frac{{\text{Weight\hspace{0.17em}of O}}_{\text{2}}}{{\text{M.W\hspace{0.17em}of O}}_{\text{2}}}=\frac{1}{32}$

${\text{No.of\hspace{0.17em}moles\hspace{0.17em}N}}_{\text{2}}=\frac{{\text{Weight of N}}_{\text{2}}}{{\text{M.W of N}}_{\text{2}}}=\frac{4}{28}$

The ratio of no. of molecules in  ${\text{O}}_2{\text{:N}}_2=\frac{(1/32)}{(4/28)}=7:32$