The isotope 12C (Carbon-12) is more likely to bond with oxygen. Carbon-12 has mass number 12 by and contains 6 protons, 6 neutrons and 6 electrons.The reason why this isotope of carbon, and not the others (c8 to C22)is that this isotope is the most abundant (98,93%). Its abundance is due to the triple-alpha process by which it is created in stars.