Oxygen-18 has an atomic number of 8. how many neutrons are in this isotope? 8 10 18 cannot be determined

Oxygen-18 is called an isotope of oxygen. The "-18" means the atomic mass of this isotope is 18. Remember, the atomic number of an atom is the number of protons it has, and the atomic mass is the number of protons plus the number of neutrons.

In the the case of oxygen-18, oxygen has an atomic mass of 18

18 = #protons + #neutrons

We know the number of protons is 8, because the atomic number is 8

18 = 8 + #neutrons

Do some algebra (subtract 8 from both sides)

#neutrons = 10