How do igneous rocks form?
a. compaction and cementation of sediment
b. cooling of molten lava or magma
c. heating and added pressure to existing rock
d. evaporation of seawater

C. Cooling of molten lava and magma

Explanation:

The rocks under the surface of earth are heated at very high temperatures. They melt at these high temperatures and create magma. Magma composition depends upon the elements of the parent rocks. It also contains gases. The elements of earth crust are main elements of magma. When this magma is cooled and hardened, igneous rocks are produced. The formation of these rocks depends upon the following factors:

i)Temperature  

ii)Pressure  

iii)Water

iv)Parent rock composition  

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