In general, Canada is a stable country.
The antonym of stable is unstable.
Iraq is somewhere between stable and unstable. Iraqi Kurdistan in particular is rather stable with minimal insurgent activity. Central Iraq is more problematic. Iraq is not a developed country, but a developing country.
Selenium is generally considered stable in its elemental form. However, some of its isotopes are unstable and undergo radioactive decay.
stable
cuba is stable
stable
Unstable.
The opposite of stable is unstable or variable.
Unstable
Radon-222 is unstable because it is a radioactive isotope with a half-life of about 3.8 days. It decays into other elements through the emission of alpha particles.
Critical Unstable Potentially Unstable Stable