The atomic number and mass of a carbon atom are 6 and 12 respectively. The model of a carbon atom is represented as follows: 

In the given model, the respective values of I and II are

The number of protons present in an atom is equal to the atomic number of the element.

The number of neutrons is the difference between the atomic mass and the atomic number of the element.

Hence, the number of protons is 6 and the number of neutrons is also 6 (12 − 6).