Which is an element hydrogen , air , carbon dioxide , water

Find the mass in grams of 1.37x1020 particles of h3po4

Ageologist determines that a sample of a mineral can't be scratched by a steel nail but can be scratched by a masonry drill bit. based on this information, the sample mineral has to be softer than a. orthoclase. b. fluorite. c. apatite. d. corundum.

Calculate the mass of 0.750 mol of the following substance. na3po4. , i'm not quite sure on how to set up the problem to solve! : (