why is the isotope of carbon c14 known as radioactive?
Carbon has 3 isptopes C-12.C-13 and C-14. 12C is 12 times heavier than hydrogen, 13C 13 times heavier. and 14C is 14 times heavier than hydrogen atom. 14C is so heavy that its nucleus is unstable and continually radiated radiation and it breaks down over time. 14C is also know as radiocarbon, because it is radioactive.