Question

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
Please select the best answer from the choices provided
A
B
C
D

Answer 1

c ) 20
because if you subtract 19 from 39 it would be 20

Answer 2

C. 20 because 39-19 is 20 so there are 20 neutrons and the atomic number is the same as number of protons and electrons.