The correct answer is option 3, glaciated areas.

A hanging valley is a geological formation that occurs as a result of glacial erosion. It is formed when a smaller glacier tributary meets a larger glacier. The smaller glacier erodes the valley floor at a slower rate compared to the larger glacier. This leads to the formation of a steep-walled U-shaped valley. When the glacier retreats or melts, the floor of the smaller valley is left higher or "hanging" above the larger valley.

Hanging valleys are commonly found in glaciated areas where there has been extensive glacial activity. These areas include high mountain ranges, such as the Himalayas and the Alps, as well as sub-Arctic regions. Hanging valleys are not typically found in coastal belts as they are not directly related to coastal processes.