A neutral atom with 6 electrons and 8 neutrons is an isotope of

It's an isotope of carbon

Explanation:

Isotopes have the same number of protons and electrons but a different number of neutrons.

Carbon, like we find it on the periodic table, has 6 electrons and protons and also 6 neutrons. (Carbon has a standard molecular weight of 12: 6electrons + 6 neutrons)

This isotope has 6 electrons but 8 neutrons, so this represents Carbon-14. Which is an isotope of carbon.