The element sodium has an atomic number of 11 and a mass number of 23. How many protons, neutrons, and electrons does one atom contain?
A) 11p+, 11e-, 12no
B) 11p+, 12e-, 11no
C) 11p+, 11e-, 23no
D) 12p+, 12e-, 11no
The atomic number is the number of protons in an element. Unless it is an ion (which I assume this isn't) the number of protons and electrons is equal. The number of neutrons is equal to the mass number (total number of particles in the nucleus) subtracted by the atomic number. Therefore you get 23-11=12. So the answer must be A).
