Some important MCQs for 12th Geology Exam with Explanation -1

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Unit 1: General Geology

1. Which of the following is a primary rock-forming mineral?
a) Quartz
b) Calcite
c) Feldspar
d) All of the above
Answer: d) All of the above
Explanation: Primary rock-forming minerals, such as quartz, calcite, and feldspar, make up the bulk of Earth's crust and are essential components of igneous, sedimentary, and metamorphic rocks. These minerals form directly during rock formation.


2. Which process involves the breaking down of rocks into smaller fragments without chemical change?
a) Weathering
b) Erosion
c) Physical weathering
d) Chemical weathering
Answer: c) Physical weathering
Explanation: Physical weathering, also called mechanical weathering, breaks rocks into smaller pieces by processes such as frost action, temperature changes, and biological activity, without altering their chemical composition.


3. The Earth’s core is primarily composed of which elements?
a) Silicon and Magnesium
b) Iron and Nickel
c) Oxygen and Aluminum
d) Carbon and Sulfur
Answer: b) Iron and Nickel
Explanation: The Earth's core consists of iron and nickel, which are dense metals. These elements sank to the center during the planet's formation due to gravitational differentiation.



Unit 2: Petrology

4. Igneous rocks are formed by:
a) Cooling and solidification of magma or lava
b) Deposition of sediments
c) Metamorphism of pre-existing rocks
d) Precipitation of minerals from water
Answer: a) Cooling and solidification of magma or lava
Explanation: Igneous rocks are formed when molten rock material (magma or lava) cools and solidifies. If cooling occurs underground, it forms intrusive rocks; if it occurs on the surface, extrusive rocks are formed.


5. Which of the following is an example of an extrusive igneous rock?
a) Granite
b) Basalt
c) Gabbro
d) Peridotite
Answer: b) Basalt
Explanation: Basalt is an extrusive igneous rock formed by the rapid cooling of lava on the Earth’s surface. Granite and gabbro are intrusive rocks, while peridotite is an ultramafic rock.


6. Metamorphic rocks with a banded or layered structure are known as:
a) Foliated rocks
b) Non-foliated rocks
c) Igneous rocks
d) Sedimentary rocks
Answer: a) Foliated rocks
Explanation: Foliated metamorphic rocks, such as schist and gneiss, exhibit a banded or layered structure due to the alignment of minerals under directed pressure during metamorphism.



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Unit 3: Structural Geology

7. The fold in which both limbs dip away from the axial plane is called:
a) Syncline
b) Anticline
c) Monocline
d) Overturned fold
Answer: b) Anticline
Explanation: In an anticline, the oldest rock layers are found at the center, and both limbs dip away from the fold axis. This is the opposite of a syncline.



8. A fault in which the hanging wall moves downward relative to the footwall is known as:
a) Reverse fault
b) Strike-slip fault
c) Normal fault
d) Thrust fault
Answer: c) Normal fault
Explanation: A normal fault occurs due to extensional forces, where the hanging wall moves downward relative to the footwall. This is common in divergent plate boundaries.


9. The term ‘isostasy’ refers to:
a) Earthquake activity
b) Balance between the Earth's crust and mantle
c) Magnetic properties of rocks
d) Movement of tectonic plates
Answer: b) Balance between the Earth's crust and mantle
Explanation: Isostasy is the state of gravitational equilibrium between the Earth's lithosphere and asthenosphere. The crust "floats" at a height dependent on its thickness and density.
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Unit 4: Paleontology

10. Which of the following is used as an index fossil?
a) Trilobites
b) Ammonites
c) Brachiopods
d) All of the above
Answer: d) All of the above
Explanation: Index fossils, such as trilobites, ammonites, and brachiopods, are species that were widespread geographically but existed for a short geological time. They help in dating rock layers.


11. The study of microfossils is known as:
a) Paleobotany
b) Micropaleontology
c) Stratigraphy
d) Geochronology
Answer: b) Micropaleontology
Explanation: Micropaleontology is the branch of paleontology that studies microscopic fossils, such as foraminifera and pollen, which are useful in understanding past environments and ages of rocks.


12. Fossils are most commonly found in which type of rocks?
a) Igneous rocks
b) Sedimentary rocks
c) Metamorphic rocks
d) None of the above
Answer: b) Sedimentary rocks
Explanation: Fossils are typically preserved in sedimentary rocks because these rocks form from the accumulation of sediments, which often include organic remains. Heat and pressure in igneous or metamorphic rocks destroy fossils.

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