WHAT is the ratio of charge to mass?e/m?

Answer 1

It is exactly what it says it is.

(The charge of something)/(The mass of the same thing)

It is most commonly applied to the electron where e/m = 1.8 x 10^11 coulombs per kg, and also things like the proton, etc:

Answer 2

ratio of charge to mass of an electron is
=1.6*10^-19 /(9.10938188*10^-31)=1.75643092*10^11



ratio of charge to mass of proton is
=1.6*10^-19 / 1.67262158*10^-27 =9.56*10^7