Helium-oxygen mixtures are used by divers to avoid the bends and are used in medicine to treat some respiratory ailments. what percent (by moles) of he is present in a helium-oxygen mixture having a density of 0.518 g/l at 25 ∘ c and 721 mmhg ?

Two students, each riding bicycles, start from the same apartment building and ride to the same building on campus, but each takes a different route. the first student rides 1100 m due east and then turns due north and travels another 1430 m before arriving at the destination. the second student heads due north for 1930 m and then turns and heads directly toward the destination.at the turning point, how far is the second student from the destination?

Most of the volume of an atom is occupied by the

What happens when a rubber rod is rubbed with a piece of fur?