Igneous rocks form by which processesheat and pressuremelting and solidifcationcompaction and cementation

Igneous rocks form by the process of melting and solidification. Here's the step-by-step process:

1. Melting: Igneous rocks begin as magma, which is molten rock deep within the earth. This magma can form when rock is heated, when pressure is reduced, or when water is added.

2. Ascent: The magma rises through the crust and may be stored in a magma chamber.

3. Cooling: As the magma rises to the surface, it starts to cool.

4. Solidification (Crystallization): As the magma cools, it begins to crystallize and form solid rock. This can happen beneath the surface (forming intrusive igneous rocks) or on the surface (forming extrusive igneous rocks).

5. Eruption: If the magma reaches the surface, it may erupt and form volcanic rocks.

6. Weathering and Erosion: Over time, these rocks may be broken down by weathering and erosion, eventually becoming sediment.

So, the correct answer to your question is "melting and solidification".