Answer:
The correct option is <u>b. rate of cooling</u>
Explanation:
The <u>magmatic rock </u>also known as the <u>igneous rock</u>, 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 <u>cooling and solidification of lava or magma.</u>
The<u> rate of cooling </u>of the melt determines the<u> texture </u>of the igneous rocks. If the cooling occurs slowly, large crystals are formed. But fast cooling results in the formation small crystals. <u>Therefore, the size of the crystal formed is determined by the rate of cooling.</u>
