Which model below represents a pure substance?

The molecular formula for caffeine is cshion402. which of the following elements is not found in caffeine?

What term is applied to a scientist who studies ancient life, including animal and plant fossils a. anthropologist b. dendroclimatologist c. geophysicist d. paleontologist

How does blood clotting prevent the entry of pathogens through cuts and wounds? answer asap,, this is due tomorrow. will mark as brainliest or whatever you call it : )