What is the mass number of a cobalt atom that has 27 protons and 30 neutrons?

• A. 57
• B. 54
• C. 27
• D. 30

Answer: (A)

Verified step by step guidance

1. Identify the number of protons in the cobalt atom, which is given as 27. This number is also the atomic number (Z) of cobalt.
2. Identify the number of neutrons in the cobalt atom, which is given as 30.
3. Recall that the mass number (A) of an atom is the sum of the number of protons and neutrons: \(A = Z + N\), where \(Z\) is the number of protons and \(N\) is the number of neutrons.
4. Substitute the given values into the formula: \(A = 27 + 30\).
5. Add the numbers to find the mass number, which represents the total number of nucleons (protons + neutrons) in the atom.