A dilute aqueous potassium nitrate solution is a homegeneous mixture.
Dilute, aqueous potassium nitrate solution is best classified as a:
(2) homogeneous mixture
A homogeneous mixture may be a solid, liquid, or volatilized mixture that has a similar proportions of its parts throughout any given sample.
Conversely, a heterogeneous mixture has parts whose proportions vary throughout the sample.
Because it's a combination of water and nitrate and you cannot clearly see the separation within the mixture .