On the periodic table, why is the mass number expressed as a decimal? * A-All atoms have half of a proton or half of a neutron in the nucleus, so decimals are necessary
B-Scientists are obsessed with small facts, so they measure atoms masses with tiny scales to get it just right
C-Elements can exist in nature with different numbers of neutrons, so the mass is an average of the isotopes that exist
D-Electrons have a very small mass, so they add decimal points to the mass of an atom.