When describing a very small chance, such as 2%, which one(s) of the following is correct?
- Highly unlikely
- Highly impossible
- Highly improbable
"Highly unlikely" and "Highly improbable" both work. They don't have number values associated with them so whether a listener thinks you mean 10%, 2% or .001% depends on the listener's own thinking and the context.
"Highly impossible" doesn't make sense. Something is either possible or impossible. There is nothing in between.