Volcanoes form in many different tectonic settings. At a mid-ocean ridge,

A. volcanoes form only on one side of the ridge.

B. lava erupts and builds up between two tectonic plates that move away from each other.

C. lava erupts and builds up between two tectonic plates that move toward each other.

D. volcanoes are unable to build up above sea level.

B.

Explanation:

Volcanoes are the molten rocks (i. e., magma) that's been erupted out of the opening of Earth's crust in the form of lava. Volcanoes along with lava also releases gases, ash and solid rocks.

Plate tectonic is a scientific theory evolved from the theory of continental drift, proposed by Alfred Wegener. This theory was fully explained in 1960s. According to this theory, scientists believe that the Earth's crust is formed with six big lithospheric plate and several smaller ones. These plates are joined together like a big puzzle and are not fixed. These plates float on half molten magma and moves along the movement of these magma. They move few centimeters per year, either towards each other or apart from each other. This movement of these plates causes Earthquakes and Volcanoes.

Volcanoes are formed at the boundaries of these tectonic plates.

The mid-ocean ridges or underwater mountains are formed from the volcanic activity. Volcanoes that are formed at mid-ocean ridge is when two plates move apart from each other. In this activity, the plates move away from each other, magma rises up between the cracks and then it cools down and gets hardened up.