Final answer:
When two tectonic plates of similar density collide, the formation of mountains is likely to occur due to the pressure that causes Earth to buckle and fold. This is exemplified by the Alps and the Appalachian Mountains. The correct answer is option a.
Step-by-step explanation:
When two tectonic plates of similar density and composition collide, the likely outcome is the formation of mountains. This occurs due to the immense pressure that causes the Earth to buckle and fold, pushing some rock deep beneath the surface while raising other areas to form mountain ranges. An example of this process is the formation of the Alps, which resulted from the collision of the African plate with the Eurasian plate. Although earthquakes and volcanic eruptions can also be associated with tectonic plate interactions, they are more characteristic of other types of plate boundaries such as divergent boundaries (seafloor spreading) or convergent boundaries with subduction (volcanic activity).
Mountain building is a significant geological process that forms linear and curved mountain belts at convergent boundaries. The Appalachian/Caledonide Mountains, for instance, were formed through multiple tectonic events and the resulting orogenies, with periods of erosion in between. Another concept related to this is isostasy, or the way the lithosphere responds to additional weight during continental collision by bending and forming foreland basins like the Persian Gulf, adjacent to the Zagros Mountains.