Volcanoes located at subduction zones tend to release lava high in content.
a. iron
b. silica
c. water
d. magma

b. silica

Explanation:

The majority of the volcanoes that form at subduction zones, or convergent plate boundaries, are stratovolcanoes. These volcanoes are also called composite volcanoes. The stratovolcanoes are known to have high to intermediate silica content of the lava they release. The eruptions tend to be periodic, and they are explosive and effusive in general, though there are exceptions. The fact that the lava is high to intermediate in silica content means that the lava is medium to highly viscous. Because of this, the lava tends to trap the gases in it, and as it reaches the surface and the temperature and pressure sharply change, the gases explode, resulting in eruptions that have lot of explosions and propelling of pyroclastic material.