The correct option is 1 and 3 only.
Explanation
Igneous rocks (derived from the Latin word ignis meaning fire) are formed by the cooling and solidification of molten rock material. They are classified as primary rocks because all other rock types are derived from them. The classification of igneous rocks is primarily based on the location where the molten material cools.
Statement-wise Analysis:
- Statement 1 is Correct: Igneous rocks are formed by the cooling and solidification of molten rock. When this molten material reaches the Earth's surface, it is termed lava. The cooling of lava forms extrusive igneous rocks. While magma (molten rock below the surface) also forms igneous rocks, the statement is factually correct as cooling lava is a primary mode of igneous rock formation.
- Statement 2 is Incorrect: If the cooling of molten material takes place at the surface, the resulting rocks are called Volcanic or Extrusive igneous rocks (e.g., Basalt). They cool rapidly, resulting in a fine-grained structure. Plutonic rocks are not formed at the surface.
- Statement 3 is Correct: If the cooling takes place at significant depths within the Earth's crust, the rocks are called Plutonic or Intrusive igneous rocks (e.g., Granite). Due to slow cooling at these depths, these rocks develop large mineral grains.
Key Takeaway:
The distinction between Plutonic (Intrusive) and Volcanic (Extrusive) igneous rocks lies in the rate and location of cooling: Plutonic rocks cool slowly deep underground (large grains), while Volcanic rocks cool rapidly on the surface (fine grains).