Mountain chains formed at divergent boundaries are called mid-ocean ridges.

Here's why:

* Divergent boundaries are where tectonic plates move apart.

* As the plates separate, magma from the Earth's mantle rises to the surface, creating new oceanic crust.

* This process builds up a long, continuous underwater mountain range called a mid-ocean ridge.

* These ridges are often characterized by volcanic activity and hydrothermal vents.

Let me know if you have any other questions!