* Atomic Number: 19. This represents the number of protons in the nucleus of a potassium atom. It's what defines potassium as potassium.
* Mass Number: This is a bit trickier because there are different isotopes of potassium. The most common isotope is potassium-39 which has a mass number of 39. This means it has 39 protons and neutrons in its nucleus. However, other isotopes exist with different numbers of neutrons, like potassium-40 and potassium-41.
Important Note: You'll often see the mass number of potassium listed as 39.1. This is the *average atomic mass* taking into account the abundance of each potassium isotope in nature.
