How many protons, neutrons, and electrons does the atom 39-K have?

How many protons, neutrons, and electrons does the atom 39-K have?

Protons = atomic number

Electrons = protons (atomic number) if the atom is neutral

Neutrons = Mass number - Number of protons (atomic number)

K has a mass number of 39 as indicated in the question and atomic number of 19 from the Periodic table. Therefore, we get 19 protons, 19 electrons and 39-19 = 20 neutrons.