Which of the following statements is false? O a. The atomic mass unit is exactly 1/12 of the mass of a carbon-12 atom O b. Both protons and neutrons have atomic masses very close to l u OC. A carbon-12 atom with six electrons has a mass of 12.6 u The atomic mass of an element is the average mass of the atoms of an element compared to an atom of d. carbon-12 at exactly 12 u To find the atomic mass of an element, you must know the atomic mass of each isotope and the fraction of each isotope in a sample