Final answer:
Most mountains form at the boundaries of tectonic plates when two continental masses collide. The pressure from the collision causes Earth's crust to buckle and fold, raising the rock to form mountain ranges.
Step-by-step explanation:
Most mountains form at the boundaries of tectonic plates when two continental masses collide. The pressure from the collision causes Earth's crust to buckle and fold, raising the rock to form mountain ranges. For example, the Alps were formed by the collision of the African and Eurasian plates. However, not all mountains are formed in the same way. On other planets, mountains can be formed by volcanic activity or large basin-forming impacts.