Final answer:
The term to describe the role of the carbon labeled with the symbol is carbon-14, denoted as ¹⁴C. It indicates an isotope of carbon with a mass number of 14 and is part of IUPAC nomenclature in chemical expressions.
Step-by-step explanation:
The term used to describe the role of the carbon labeled with the symbol is carbon-14. Labelling a radioactive isotope, such as carbon-14, involves using the chemical symbol for carbon (C), with the atomic number as a subscript and the mass number as a superscript. For example, the notation ¹⁴C indicates carbon with 6 protons (atomic number) and 8 neutrons (14 minus 6 protons), giving it the mass number 14. This notation can also be expressed as "carbon-14", which explicitly specifies the isotope of carbon with the mass number 14.
In IUPAC nomenclature, the position labels of carbon atoms in a chain are often indicated by numerical superscripts, but when discussing specific isotopes, the notation reflects the mass number as well. Furthermore, carbon atoms can be labeled in different ways depending on the naming system used, such as using Greek letters in trivial nomenclature or ω-minus labels for unsaturated fatty acids.