[tex]\nu_{C_3H_8}=\frac{40.4}{\mu_{C_3H_8}}=[/tex]
[tex]=\frac{40.4}{3A_C+8A_H}=\frac{40.4}{44}=[/tex]
[tex]=\frac{9}{10}=0.9mol[/tex]
[tex]1mol\ C_3H_8...5\ mol\ O_2 \\ 0.9mol\ C_3H_8...x\ mol\ O_2[/tex]
[tex]x=\frac{0.9*5}{1}=4.5mol\ O_2[/tex]
[tex]m=\mu_{O_2}*x=2*A_O*4.5=9*8=72g\ O_2[/tex]