試題詳解

81. A sample of helium gas has been contaminated with argon gas. At 1 atm and 25°C, the density of the mixture is 0.200 g/L. What is the volume percent helium in the sample?
(A) 90.0%
(B) 97.5%
(C) 80.3%
(D) 2.5%
(E) 99%