The answer are: mountains are formed, crust become molten rock and denser plates slides under lighter plates.
Let's look into the options one by one:
Crust is formed.
-This is in correct.
-At the ocean trench, plates subducts and were destroyed. No process of construction occurs as it is located at a destructive plate boundary.
Mountains are formed.
- This is correct.
- As it is located in the destructive plate bondary, two plates collide and create compressional force. The lighter continential will be compressed and foldes up to form fold mountains. One of the examples is the Rocky Mountain.
Seafloor spreading occurs.
-This is incorrect.
- Seafloor spreading occurs at constructive plate boundaries, however ocean trench occurs at destructive plate boudary and thus seafloor spreading does not take place.
Crust becomes molten rock.
- This is correct.
- When ocean trench is formed, denser oceanic plate subducts under the less dense continental plate and meets the hot magma. The crust material will then melt under high temperature and become molten rock.
Denser plates slide under lighter plates.
- This is correct.
- At deep ocean trenches, denser oceanic plate slide under the lighter continential plate as it is located the destructive plate boundary.
It might not be on time, but I hope it helps explain the question. :)
