How many zeros are in the measurement 0.000040200 m are significant?

Where are each of the three particles located within the atom?

In the millikan oil drop experiment they determined that every drop had a charge which was a while number multiple of -1.60x10^-19. if a drop has a total charge of -9.60x10^-19 then how many excess electrons are contained within the drop?

What is the empirical formula for c4h8o2