An atom with an atomic mass of 89 and an atomic number of 39 has how many neutrons?

• A. 50
• B. 89
• C. 28
• D. 39

Answer: (A)

Verified step by step guidance

1. Identify the atomic number (Z) and the atomic mass number (A) from the problem. The atomic number is the number of protons, and the atomic mass number is the total number of protons and neutrons in the nucleus. Here, the atomic number is 39 and the atomic mass is 89.
2. Recall the relationship between atomic mass number, protons, and neutrons: \(A = Z + N\), where \(N\) is the number of neutrons.
3. Rearrange the formula to solve for the number of neutrons: \(N = A - Z\).
4. Substitute the given values into the equation: \(N = 89 - 39\).
5. Calculate the difference to find the number of neutrons in the atom.