300
subatomic particle:
A. the weighted averages of the masses of an element's isotopes (naturally occurring isotopes of course)
B. the tinier parts of an atom; protons, neutrons, and electrons
C. natural and human-made substances that cannot be broken down into simpler substances through chemical reactions
D. classifying chart for natural and human-made elements
the tinier parts of an atom, protons, neutrons, and electrons