Which of the following correctly describes an atom with 8 protons, 9 neutrons, and 10 electrons?

• A. A fluorine atom (F) with a mass number of 17
• B. A sodium ion (Na^{+}) with a mass number of 17
• C. A neutral oxygen atom with a mass number of 17
• D. An oxide ion (O^{2-}) with a mass number of 17

Answer: (D)

Verified step by step guidance

1. Identify the element by the number of protons, since the atomic number (Z) equals the number of protons. Here, the atom has 8 protons, so the element is oxygen (O), which has atomic number 8.
2. Calculate the mass number (A) by adding the number of protons and neutrons: \(A = \text{protons} + \text{neutrons} = 8 + 9\).
3. Determine the charge of the atom or ion by comparing the number of protons and electrons. Since there are 8 protons and 10 electrons, the net charge is \$8 - 10 = -2$, indicating a 2- charge.
4. Match the charge and element to the correct species. An oxygen atom with 2 extra electrons is an oxide ion, written as \(\mathrm{O}^{2-}\).
5. Confirm the mass number matches the sum of protons and neutrons (17), and that the species is an oxide ion with a mass number of 17, which fits the description given.