Bismuth has an atomic number of 83 and its most common isotope has a mass number of 209. How many neutrons are present in this isotope of bismuth?

• A. 83
• B. 126
• C. 292
• D. 209

Answer: (B)

Verified step by step guidance

1. Identify the atomic number (Z) of bismuth, which is given as 83. The atomic number represents the number of protons in the nucleus of the atom.
2. Note the mass number (A) of the isotope, which is given as 209. The mass number is the total number of protons and neutrons in the nucleus.
3. Recall 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 the number of neutrons: \(N = A - Z\).
5. Substitute the known values into the equation: \(N = 209 - 83\), which will give the number of neutrons in this isotope of bismuth.