Question

How do scientists determine the number of neutrons in an isotope of an atom?

Answer 1

D.  The atomic mass in amu is basically the number or nuclei since the mass of the electrons is negligible.  For a given atom (element) the number of protons is fixed.  Say the element has 10 protons.  If the atomic weight is 14 atomic mass units (amu), you know that there are 4 neutrons, since both neutrons and protons are 1 amu each and there are 10 protons