In the figure attached, a plot of the problem is shown.
Location 1 and 4 are likely to have subatomic particles with the least mass because they are not in the nucleus, which is the location with most of the mass of the atom.
Mass is most concentrated in the nucelus of an atom. Therefore, if you are looking to find the area with the least mass, go outside of the nucelus. Points one and four are the furthest outside of the nucleus.
