Which of the following rocks is produced by the solidification of magma within the earth crust?

Step 1: Analyze the question The question asks which rock forms when magma solidifies within the earth's crust (not on the surface).

Step 2: Explain the concept Rocks are grouped by how they form:

• Igneous rocks form from cooled and solidified magma or lava. They are divided into two types: • Intrusive (plutonic) rocks: magma cools slowly beneath the surface, inside the crust. The slow cooling gives large crystals. Examples: granite, gabbro, diorite. • Extrusive (volcanic) rocks: lava cools quickly on the surface. This gives small crystals or a glassy texture. Examples: basalt, obsidian, pumice.
• Sedimentary rocks form from the deposition and compaction of sediments (e.g. sandstone, limestone).
• Metamorphic rocks form when existing rocks are changed by heat and pressure (e.g. marble, slate).

Step 3: Solve by elimination

• A. Plutonic rock: forms from magma that solidifies deep within the crust. ✔
• B. Metamorphic rock: formed by changes to existing rock, not by magma solidifying. ✘
• C. Sedimentary rock: formed from sediments. ✘
• D. Extrusive rock: formed from lava that solidifies on the surface, not within the crust. ✘

Answer: Plutonic rock, which is option A.

Tip: Think of "Pluto," the god of the underworld. Plutonic = deep underground (intrusive), while extrusive = exits onto the surface. Also remember that magma is molten rock below the surface, and lava is molten rock above it.