Question

1. a mixture separates into layers over time. this is a select .

Explanation:

The problem is about a mixture separating into layers, which relates to the properties of mixtures in Chemistry (a subfield of Natural Science). A heterogeneous mixture, specifically a suspension or immiscible liquid mixture, separates into layers over time due to differences in density or immiscibility. So the term for this is a "heterogeneous mixture" (or more specifically, if it's liquids, an "immiscible mixture" or "suspension" depending on components, but the key concept is heterogeneous as it has distinct layers).

Answer:

heterogeneous mixture (or immiscible mixture, suspension - depending on context, but heterogeneous mixture is the broad term for mixtures with non - uniform composition and visible layers)