Final answer:
A carbon atom with an atomic number of 6 has 6 protons and, if its mass number is 12, it has 6 neutrons. The first electron level holds 2 electrons, while the second holds 4 electrons.
Step-by-step explanation:
The atomic number of carbon is 6, which indicates that there are 6 protons in the nucleus of a carbon atom. If the carbon atom has a total of 12 particles in its nucleus, and knowing that it has 6 protons, the atom must have 6 neutrons to make up the remainder. For the electron arrangement, the first energy level of the carbon atom can hold a maximum of 2 electrons, while the second level can hold up to 4 electrons. So, in a neutral carbon atom, the first level has 2 electrons and the second level has 4 electrons.