A mixture of methane and ethane in the molar ratio of x:y has a mean molar mass of 20. what would be the mean molar mass, if the gases are mixed in the molar ratio of y:x?

Options

A. 20
B. 22
C. 24
D. none of these

Answer

C

Explanation

Mean molecular mass
`=20=(16x+28y)/(x+y) implies x = 2y` ...(i)
Mean molecular mass in the second case `=(28x+16y)/(x+y)=?` ...(ii)
x = 2y
`:. (28x+16y)/(x+y)=(28 xx 2y xx 16y)/(2y+y)=(72y)/(3y)=24`