If a mixture looks smooth and the same throughout, what is it most likely?
A homogeneous mixture.
Otherwise referred to as a solution, a homogeneous mixture is one of the two types of mixtures (the other being a heterogeneous mixture).
Some examples of homogeneous mixtures include:
City air (it has to be city air because pure air would not be a mixture, rather a pure substance)
Tap water (again, it has to be tap water because pure and distilled water would be a pure substance)
As you can see, both these examples look 'smooth' and same throughout.
For reference, I'll provide some examples of heterogeneous mixtures.
Soil (the dirt can be composed over many different things, including sediments, rock, insects, etc, etc.)
Salad (this is because salads include different types of vegetables, fruits, sauces, etc, etc.)