Which rocks are commonly formed as a result of volcanic eruptions?

The correct choice is igneous rocks because these types of rocks are formed directly from the solidification of molten material called magma. When a volcanic eruption occurs, magma erupts onto the surface and is called lava. As the lava cools and solidifies, it forms igneous rocks.

There are two main types of igneous rocks: intrusive (or plutonic) rocks, which form when magma cools slowly beneath the Earth's surface, and extrusive (or volcanic) rocks, which form when lava cools quickly on the surface. Common examples of extrusive igneous rocks include basalt and pumice.

Metamorphic rocks, sedimentary rocks, and crystalline rocks do not form from volcanic activity. Metamorphic rocks are produced under heat and pressure from pre-existing rocks, sedimentary rocks form from the accumulation of sediment, and crystalline rocks typically refer to a texture of certain minerals rather than a specific type of rock formation process. Thus, igneous rocks are indeed the product of volcanic activity, making them the correct answer.