Consider two isotopes of the element potassium. The atomic number of potassium is 19. One isotope has the atomic mass 39 while t
he other isotope has the atomic mass 40. Which of the following statements about the isotopes is correct?
One isotope contains 39 protons while the other contains 40 protons
One isotope contains 20 protons while the other isotope contains 19 protons.
Both isotopes contain 20 protons.
One isotope contains 20 neutrons while the other isotope contains 21 neutrons
