Question

When a soft drink is left open and allowed to lose all of its carbonation, is it still a homogeneous mixture?

Answer 1

Hey.
Forget the chemistry and focus more into the physical appearance.
Homogenous mixture is the one where we can only see one phase.
When a drink like Coca-Cola is left open for some time, you see that the bubbles may be gone and you most likely see a black liquid only.
Therefore, that will be a homogeneous mixture.