How many neutrons are there in the ion 18O−2 ?A. 8B. 10C. 16D. 20

The number of neutrons in an atom can be found by subtracting the atomic number (number of protons) from the atomic mass number (number of protons + number of neutrons).

For the oxygen isotope 18O, the atomic mass number is 18. The atomic number of oxygen, which represents the number of protons, is 8.

So, to find the number of neutrons, we subtract the atomic number from the atomic mass number:

18 (atomic mass number) - 8 (atomic number) = 10 neutrons

Therefore, the correct answer is B. 10.

Note: The charge of the ion (-2) does not affect the number of neutrons. It only indicates that there are two more electrons than protons.