In atomic structure, how do you determine the mass number (A) of an element’s atom?

• A. Add the number of protons and neutrons in the nucleus: $A=Z+N$.
• B. Add the number of protons and electrons: $A=Z+e$.
• C. Subtract the number of neutrons from the number of protons: $A=Z-N$.
• D. Use the atomic number only: $A=Z$.

Answer: (A)