Which of the following is an example of intrusive igneous rock?

Granite is an example of intrusive igneous rock because it forms from the slow crystallization of magma beneath the Earth's surface. This gradual cooling allows large mineral crystals to develop, which is characteristic of intrusive igneous rocks. Granite typically contains visible grains of minerals such as quartz, feldspar, and mica, and its formation occurs over a long period of time, giving it a coarse-grained texture.

In contrast, basalt is an example of extrusive igneous rock, as it forms from lava that cools quickly at the Earth's surface, resulting in a fine-grained texture. Obsidian, another extrusive rock, is a volcanic glass that forms rapidly from the cooling of lava. Silica rock is not directly classified as igneous but rather refers to rocks that contain high amounts of silica, which can be associated with various types of rocks, including sedimentary ones. Thus, granite uniquely fits the criteria for intrusive igneous rock among the given options.