What defines the size of an atom

Every atom is different in its number of protons, its mass, and its size. The size of the atoms is determined by the size of their orbitals. The larger the quantum number "n" is, the larger the orbital is, which increases the size of the atom

answers: to make sure that all of the broken pieces of tablet were added to the water, to allow for fair comparison of all three trials, with different particle sizes to avoid experimental error

i think it's c. if you look search electronic symbol on google and then click on wiki it shows you a