The most abundant isotope of carbon is carbon-12 (C-12), which constitutes about 98.89% of all carbon found in nature. Carbon-12 has six protons and six neutrons in its nucleus, making it stable and non-radioactive. It plays a critical role in organic chemistry and biochemistry since it forms the backbone of most organic molecules, including carbohydrates, proteins, and fats. Carbon-12 is significant for understanding biological processes, such as photosynthesis, where it is incorporated into glucose. Its stability and abundance make it crucial for life as we know it.