19 protons 18 electrons and 19 neutrons
Proton = 19
electron = 19
neutron = 20
electron = 19
neutron = 20
Look it up on a dang periodic table, and you need to know the isotope of potassium you are talking about as the number of neutrons depends on the mass. The atomic number is the number of protons in the nucleus of that atom, the number of electrons should be this number as well as long as it is a neutral atom and not an ion.