How many neutrons are present in an atom of fluorine-19?

• A. 9
• B. 10
• C. 18
• D. 19

Answer: (B)

Verified step by step guidance

1. Identify the atomic number (Z) of fluorine, which is the number of protons in the atom. For fluorine, Z = 9.
2. Recognize that the isotope notation fluorine-19 indicates the mass number (A) of the atom, which is the total number of protons and neutrons. Here, A = 19.
3. Use the relationship between mass number, protons, and neutrons: \(A = Z + N\), where \(N\) is the number of neutrons.
4. Rearrange the formula to solve for neutrons: \(N = A - Z\).
5. Substitute the known values: \(N = 19 - 9\), which gives the number of neutrons in fluorine-19.