Question

Why carbon-12 is an isotope of carbon?

Answer 1

Because elemental carbon has several isotopes. All carbon nuclei possess 6 protons, but some carbon nuclei possess more than 6 neutrons.

Explanation:

All carbon nuclei have the same atomic number, `Z`, the number of protons in the nucleus. For `C, Z = 6`, i.e. there are 6 protons in the carbon nucleus. If there were not 6 protons in the nucleus, the element would not be `C`. Most carbon nuclei have 6 neutrons; however, there are a very small percentage that have 7 or 8 neutrons, or even more neutrons. Approx. 99% of all carbon nuclei are carbon-12. It is the number of protons that determine the atomic number, that is the element's identity.