What is the name of the stable carbon isotope with 7 neutrons?

The stable carbon isotope with 7 neutrons is carbon-13.

Carbon’s atomic number is 6, so every carbon isotope has six protons. An isotope’s name gives its mass number—the total of protons and neutrons. Six protons plus seven neutrons equals 13, producing carbon-13, written ¹³C or carbon-13.

Carbon-13 is naturally occurring and stable, unlike carbon-14, which is radioactive and is used in radiocarbon dating. The most abundant carbon isotope is carbon-12, with six protons and six neutrons. Carbon-13 makes up roughly 1.1% of natural carbon, so it is uncommon but plentiful enough to detect.

That small abundance has major scientific value. In mass spectrometry, molecules containing carbon-13 can create an M+1 peak. Enriched carbon-13 compounds are also used in nuclear magnetic resonance, metabolic tracing, environmental studies, and the carbon-13 urea breath test. Carbon-11 is a radioactive isotope used in some medical imaging, making it a particularly easy distractor.