The thickest part of the crust occurs in ocean basins rift zones young mountain ranges older eroded mountain ranges

Option (3)

Explanation:

The continental crust is usually thick because it has an average thickness of about 35-40 km. In the high mountain ranges, it is the thickest, forming about 80 km on an average. These are formed when two continental plates form a sandwich pattern by sharing a convergent type of plate boundary.

For example, the thickest part of the crust is the Mt. Everest which lies in the great Himalayan range, which has started to form about 50 million years back. It is geologically the most recent mountain range.

The older mountains are continuously eroded in the geological past, as a result of which the height of the mountains is affected.

Thus, the correct answer is option (3).