Answer:
Mass number of carbon is 12.
Explanation:
Carbon atom is defined as 6 atoms in a nucleus, and the mass number is the total number of protons and neutrons in the nucleus of an atom.
Before any neutrons are added to the carbon atom, its mass number is 6; after 6 neutrons are added, the total number of protons and neutrons is now 12—the mass number becomes 12.
