Atoms of the same element can have different atomic masses because they can have different numbers of A electrons B neutrinos C neutrons D protons

C neutrons

Explanation:

Elements can have isotopes, which are atoms with different atomic masses. They have the same number of protons but different number of neutrons.

the old alchemists made significant contributions to science even though there starting premises were off a bit. their conclusions after failure would steer them into better directions for investigation. science is no more than close observation and the initial mistakes result in rethinking and retrying experiments.