The element that has known isotopes with masses of 12 amu, 13 amu, and 14 amu is carbon. These isotopes are:
- Carbon-12 (^12C)
- Carbon-13 (^13C)
- Carbon-14 (^14C)
Carbon-12 is the most abundant isotope, while Carbon-14 is radioactive and is commonly used in radiocarbon dating.