Three naturally occurring isotopes of carbon exist: The atomic mass of carbon is 12.01 amu. Which of the three carbon isotopes is most abundant in nature?
A) carbon-12
B) carbon-13
C) carbon-14
D) all three occur with equal abundance
The correct answer and explanation is :
The correct answer is A) carbon-12.
Explanation:
Carbon exists in nature as three stable isotopes: carbon-12 (¹²C), carbon-13 (¹³C), and carbon-14 (¹⁴C). These isotopes differ in the number of neutrons in their nuclei. Carbon-12 has 6 protons and 6 neutrons, carbon-13 has 6 protons and 7 neutrons, and carbon-14 has 6 protons and 8 neutrons.
- Carbon-12 (¹²C):
- Carbon-12 is by far the most abundant isotope of carbon in nature, accounting for about 98.93% of the carbon found on Earth. Its abundance is due to the fact that it is a stable isotope with no radioactivity. Since carbon-12 is the most stable, it is the most commonly found in both organic and inorganic compounds.
- Carbon-13 (¹³C):
- Carbon-13 makes up around 1.07% of natural carbon. It is also stable and has one more neutron than carbon-12. It is used in various applications, such as in stable isotope labeling in research, but is much less abundant than carbon-12.
- Carbon-14 (¹⁴C):
- Carbon-14 is a radioactive isotope of carbon, and although it is present in trace amounts (approximately 0.0000000001% of natural carbon), it is crucial in radiocarbon dating. It decays over time, which is why it is used in dating ancient organic materials, as it has a half-life of about 5,730 years.
The atomic mass of carbon is about 12.01 amu because it is a weighted average of the masses of its isotopes, where carbon-12 contributes the most, followed by carbon-13 and a small fraction of carbon-14. Since carbon-12 is overwhelmingly the most abundant isotope, it gives carbon its characteristic atomic mass.
