Question

The main difference between intrusive and extrusive igneous rocks is ___?

Answer 1

The correct answer is A. Intrusive is due to magma cooling deep within Earth's surface and extrusive is due to it cooling at Earth's surface.

The intrusive rocks are forming deep bellow the surface, and they cool off very slowly. Because of that they are forming big crystals.
The extrusive rocks are forming on the surface, and they cool off very quickly. Because of that they are forming small crystals.