Igneous rock forms when magma cools. Here's an explanation:
1. Magma is molten rock beneath the Earth's surface. When this magma cools down and solidifies, it forms igneous rock.
2. Igneous rocks can be classified into two main types: intrusive igneous rocks, which cool below the Earth's surface and have larger crystals due to slower cooling, and extrusive igneous rocks, which cool on the Earth's surface and have smaller crystals due to rapid cooling.
3. Examples of igneous rocks include granite, basalt, and obsidian.
So, the correct answer to the question "What type of rock forms when magma cools?" is OD. Igneous.
