An atom of potassium has an atomic mass of 39 amu and an atomic number of 19. It therefore has ______ neutrons in its nucleus.
a. 19
b. 39
c. 20
d. 2
39-19 = 20
To determine the number of neutrons in an atom of potassium, we can subtract the atomic number from the atomic mass.
In this case, the atomic mass of potassium is 39 amu and the atomic number is 19.
So, the number of neutrons in the potassium atom would be:
39 amu - 19 = 20 neutrons
Therefore, the correct answer is (c) 20.