What is meant by saying that carbon-12 is stable?

Question

What is meant by saying that carbon-12 is stable?
an also why is the number of nuclei is 25957922978 why this suggest that the salt is heavily contaminated?

Answer 1

Stable means Carbon-12 does not decay by a radiation process into another element. Carbon-14 is unstable, and decays by beta emission into Nitrogen 14.

I'm not sure what your second quaetion is asking.