Final answer:
A solution is a homogeneous mixture like salt in water, where components are indistinguishable, while a heterogeneous mixture such as sand in water has visibly distinct parts.
Step-by-step explanation:
The key difference between a solution and a heterogeneous mixture lies in their uniformity. A solution is a homogeneous mixture where two or more substances are mixed so thoroughly that they appear as a single substance. An example of a solution is salt dissolved in water; no matter how closely you observe, you cannot see the individual particles of salt once they have dissolved. On the other hand, a heterogeneous mixture is non-uniform, and its different components can be identified. An example of a heterogeneous mixture is a combination of sand and water, where you can see the separate particles of sand within the water.