## Chemistry and Chemical Reactivity (9th Edition)

According to the periodic table, Mn has 25 protons. With a mass of 54.9380u, and the masses of the proton and neutron being 1.007276u and 1.008665u respectively: $54.9380=25\times1.007276+n^0\times1.008665$ $n^0=29.5\approx30$