Some important MCQs with explanations related to General Geology for the Jharkhand Academic Council (JAC) 12th Exam -2

16. Which of the following is the primary cause of earthquakes?

a) Volcanic eruptions

b) Tectonic plate movements

c) Erosion of mountains

d) Meteorite impacts

Answer: b) Tectonic plate movements

Explanation:

Earthquakes are primarily caused by the movement of tectonic plates along faults, which release energy in the form of seismic waves.

---

17. What is the term for the process by which rocks break down due to environmental factors?

a) Lithification

b) Weathering

c) Erosion

d) Metamorphism

Answer: b) Weathering

Explanation:

Weathering refers to the breakdown of rocks into smaller particles through physical, chemical, or biological processes.

---

18. Which type of boundary occurs when two tectonic plates move towards each other?

a) Divergent boundary

b) Transform boundary

c) Convergent boundary

d) Lateral boundary

Answer: c) Convergent boundary

Explanation:

Convergent boundaries occur where two tectonic plates move toward each other, often resulting in mountain formation, subduction zones, or volcanic activity.

---

19. What is the Earth’s lithosphere?

a) The inner core

b) The rigid outer layer of the Earth

c) The fluid outer layer of the Earth

d) The mantle beneath the crust

Answer: b) The rigid outer layer of the Earth

Explanation:

The lithosphere is the outermost shell of the Earth, including the crust and the uppermost part of the mantle, which is rigid and breaks into tectonic plates.

---

20. Which of the following rocks is formed through cooling and solidification of lava?

a) Granite

b) Basalt

c) Limestone

d) Gneiss

Answer: b) Basalt

Explanation:

Basalt is an extrusive igneous rock that forms when lava cools rapidly at or near the Earth's surface.

---

21. What is the primary characteristic of metamorphic rocks?

a) They form from cooling and solidification of magma.

b) They are composed of sediments from pre-existing rocks.

c) They are formed by heat and pressure.

d) They are rich in fossils.

Answer: c) They are formed by heat and pressure.

Explanation:

Metamorphic rocks form when existing rocks (igneous, sedimentary, or other metamorphic rocks) are subjected to heat and pressure, leading to physical or chemical changes.

---

22. Which of the following best describes a fault?

a) A type of sedimentary rock

b) A large igneous intrusion

c) A fracture in the Earth's crust along which movement has occurred

d) A type of mineral deposit

Answer: c) A fracture in the Earth's crust along which movement has occurred

Explanation:

A fault is a crack or fracture in the Earth's crust where movement has occurred, typically associated with seismic activity.

---

23. What is the main difference between an intrusive and extrusive igneous rock?

a) Intrusive rocks form on the surface, extrusive rocks form underground.

b) Intrusive rocks are formed by cooling of magma beneath the surface, while extrusive rocks cool from lava at the surface.

c) Intrusive rocks have larger crystals than extrusive rocks.

d) Extrusive rocks contain more minerals than intrusive rocks.

Answer: b) Intrusive rocks are formed by cooling of magma beneath the surface, while extrusive rocks cool from lava at the surface.

Explanation:

Intrusive rocks (like granite) form below the Earth's surface, cooling slowly and resulting in larger crystals, while extrusive rocks (like basalt) form at the surface and cool quickly, resulting in smaller crystals.

---

24. What is the main cause of volcanic eruptions?

a) Tectonic plate movements

b) Cooling of magma

c) Gas pressure from molten rock

d) Seismic activity

Answer: c) Gas pressure from molten rock

Explanation:

Volcanic eruptions occur when pressure from gases within molten rock exceeds the strength of the surrounding rock, causing the magma to escape to the surface.

---

25. What is the process by which rocks are subjected to high heat and pressure, causing changes in their mineral composition and structure?

a) Erosion

b) Metamorphism

c) Lithification

d) Sedimentation

Answer: b) Metamorphism

Explanation:

Metamorphism is the process by which pre-existing rocks are altered due to high heat, pressure, or chemically active fluids, leading to changes in texture and mineral composition.

---

26. Which of the following is an example of a sedimentary rock?

a) Granite

b) Basalt

c) Sandstone

d) Schist

Answer: c) Sandstone

Explanation:

Sandstone is a sedimentary rock formed from compacted sand grains, typically deposited in water or wind.

---

27. What is the primary difference between a primary and secondary wave (P-wave and S-wave) during an earthquake?

a) P-waves travel faster than S-waves.

b) S-waves are longitudinal, and P-waves are transverse.

c) P-waves cannot travel through liquids, while S-waves can.

d) S-waves are more destructive than P-waves.

Answer: a) P-waves travel faster than S-waves.

Explanation:

P-waves (primary waves) are compressional and travel faster than S-waves (secondary waves), which are shear and slower. P-waves can travel through both solids and liquids, while S-waves only move through solids.

---

28. What type of rock forms from the cooling and solidification of magma beneath the Earth’s surface?

a) Metamorphic

b) Sedimentary

c) Igneous

d) Organic

Answer: c) Igneous

Explanation:

Igneous rocks form from the cooling and solidification of magma or lava. Intrusive igneous rocks, like granite, form beneath the surface, while extrusive igneous rocks, like basalt, form on the surface.

---

29. Which rock type is most likely to contain fossils?

a) Metamorphic rock

b) Igneous rock

c) Sedimentary rock

d) Volcanic rock

Answer: c) Sedimentary rock

Explanation:

Sedimentary rocks, such as limestone and shale, often contain fossils because they form from the accumulation and compression of sediment, preserving ancient organisms.

---

30. Which of the following is not a type of plate boundary?

a) Convergent

b) Divergent

c) Transform

d) Lateral

Answer: d) Lateral

Explanation:

The three main types of plate boundaries are convergent (plates move toward each other), divergent (plates move apart), and transform (plates slide past one another). "Lateral" is not a recognized type of plate boundary.