Which of the following correctly identifies the composition of an oxygen atom?

A. 8 protons, 8 electrons, and 8 neutrons

B. 6 protons, 6 electrons, and 8 neutrons

C. 8 protons, 6 electrons, and 7 neutrons

D. 6 protons, 6 electrons, and 12 neutrons

Oxygen has the atomic number 8, which eliminates options B and D right away. Any neutral atom, including the oxygen atom, has the same number of protons and electrons, meaning the number of electrons is also 8. If you're still not sold, the oxygen atom has a mass number of 16, which is the sum of the protons and neutrons in the atom, meaning there have to be 8 neutrons as well. The answer is option A.

The answer is A. The atomic number of oxygen is 8 so it has 8 protons and the same number of electrons to balance the charge, making it neutral. Lastly, its atomic mass is about 16 so it has 8 neutrons. Atomic mass is protons + neutrons.