A gas mixture has a total pressure of 855 mm Hg and the gas mixture is comprised of 25 g of fluoroform, HCF3 and 15.0 g of O2. What is the partial pressure of oxygen?

True, the standard unit for volume is liters which can be represented by either a lower case "l" or a capital "l"

C) electrons encircling a nucleus with neutrons and protons

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).