How does equation below demonstrate the law of conservation of mass?

One of the following properties was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version. which property fits this description?

Identify the missing numbers below to show the result of multiplying the numbers (1.6 × 10-19)(5.0 × 106) = c × 10d

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?