carbon has an average atomic mass of 12.011 amu (as given on the periodic table). Which isotope of carbon do you think is more abundant: carbon-12 or carbon-13? Explain your answer. Check your answer by using the sim to select carbon and clicking on "Nature's mix of isotopes".

Carbon-12 would be most abundant because the amu is 12.011, indicating that the average leans toward the carbon-12 isotope instead of the carbon-13 isotope. If the amu would have been 12.99, you could say that carbon-13 is more aboundant becasue the average is closer to the carbon-13 isotope.