Answer:
The correct option is b. rate of cooling
Explanation:
The magmatic rock also known as the igneous rock, is one of the three principal rock types, sedimentary, igneous and metamorphic.
The igneous rocks are also called primary rocks, as they crystallize from a liquid. They are formed by the process of cooling and solidification of lava or magma.
The rate of cooling of the melt determines the texture of the igneous rocks. If the cooling occurs slowly, large crystals are formed. But fast cooling results in the formation small crystals. Therefore, the size of the crystal formed is determined by the rate of cooling.
