The chemical properties of ANY atom are found in how they react with other elements.
A. An element's symbol - Nothing to do with reactions
B. The average atomic mass -The mass doesn't react
C. The number of electrons that occupy the outer shell - the only part of the electrons that move, SO they are involved in the reactions (answer)
D. The total number of electrons - The inner electrons cannot move from the atom unless there is ALOT of energy given to them, so these cannot react and would not contribute to the chemical properties.