Volcanoes that form along mid-ocean ridges occur at divergent plate boundaries.

Here's why:

* Mid-ocean ridges are underwater mountain ranges where new oceanic crust is created.

* Divergent plate boundaries are areas where tectonic plates move apart.

* As the plates pull away from each other, magma from the Earth's mantle rises to the surface and erupts, creating new crust and forming volcanoes.

This process is known as seafloor spreading, and it's a key part of plate tectonics.