Answer:
20 approximately.
Step-by-step explanation:
There are two variables that you could use to calculated: Atomic Number and Atomic Mass.
Atomic number refers to the number of protons that the atom has.
Atomic mass refers to the whole: protons and neutrons.
If we subtract: Atomic mass - Atomic Number = Number of protons.
For potassium (K):
Atomic number: 19
Atomic mass: 39.09. (we round the number for the subtract).
So, 39 - 19 = 20.
20 PROTONS. Approximately.