Question

what geologic feature/event would you most likely to find at a divergent boundary between two pieces of oceanic crust? island arc mid-ocean ridge flat land rift valley

Explanation:

A divergent boundary between two pieces of oceanic crust is a place where tectonic plates move apart. Mid - Ocean Ridges form at such boundaries as magma rises to fill the gap, creating new oceanic crust. Island Arcs form at convergent boundaries (subduction zones). Flat land is a general term not specific to this boundary type. Rift Valleys are more associated with continental divergent boundaries.

Answer:

Mid - Ocean Ridge