* Heterogeneous mixtures have components that are not uniformly distributed throughout. You can see the different parts of the mixture.

* Homogeneous mixtures have components that are evenly distributed, creating a uniform appearance.

Marshmallows are made of sugar, gelatin, and air. When you dissolve a marshmallow in water, the sugar dissolves, but the gelatin and air don't. You'll end up with a mixture where you can see distinct parts: dissolved sugar, undissolved gelatin, and air bubbles.

Therefore, a marshmallow solution is not a uniform mixture and is considered heterogeneous.