Question 3
An atom has a mass number of 14 and an atomic number of 6. How many electrons does it contain?
The right answer is the one marked above.
6. The atomic number is the number of protons, and in a neutral atom the electrons equal the protons.
8 is the neutron count — that is A − Z = 14 − 6. The mass number says nothing directly about electrons, because the electrons are too light to count towards the mass at all. This atom is carbon, since only carbon has Z = 6.