Question

12.15--atmosphere practice p.1
radio waves bounce off part of this layer

Explanation:

The question is about the atmospheric layer where radio waves bounce off. In atmospheric science (a subfield of Natural Science, specifically Geography or Environmental Sciences - related to atmospheric layers), the ionosphere (part of the thermosphere or sometimes considered a separate layer) reflects radio waves. The layer associated with radio wave reflection is the ionosphere, and the thermosphere contains the ionosphere. But more precisely, the ionosphere (often part of the thermosphere) or the thermosphere's ionized part. However, the main layer where radio waves bounce is the ionosphere, which is part of the thermosphere. But in basic atmospheric science, the answer is the ionosphere, and the layer structure: the thermosphere has the ionosphere, but the key layer for radio wave reflection is the ionosphere (or sometimes the thermosphere is mentioned, but ionosphere is more specific). Wait, actually, the correct layer where radio waves bounce off (reflect) is the ionosphere, which is a region within the thermosphere (and also mesosphere - ionosphere overlap? No, mainly thermosphere). But in standard atmospheric layers, the ionosphere (part of the thermosphere) reflects radio waves. So the answer is the ionosphere (or thermosphere, but ionosphere is the region with ions that reflect radio waves).

Answer:

Ionosphere (or Thermosphere, as the ionosphere is part of the thermosphere)