It's not a molecule, it is an element

The most common isotope of carbon is carbon-12.

The most common isotope of carbon is carbon-12.

The most common isotope of carbon is carbon-12.

The most common isotope of carbon is carbon-12.

carbon -12 is the most common isotope of carbon.

98.9% of all carbon is Carbon-12

So, if you find some carbon. charcoal diamond or any other form of carbon, I am 98.9%sure it is C-12.

Carbon-12 has a mass number of 12.

carbon 14 is a isotop of carbon 12.