Some important MCQs with explanations related to General Geology for the Jharkhand Academic Council (JAC) 12th Exam -1

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1. What is the Earth's outermost layer called?

a) Mantle
b) Core
c) Crust
d) Lithosphere

Answer: c) Crust
Explanation:
The Earth's crust is its outermost layer, composed primarily of silicate rocks. It is divided into continental and oceanic crust.


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2. Which type of rock is formed from cooling and solidification of magma or lava?

a) Sedimentary
b) Metamorphic
c) Igneous
d) Fossiliferous

Answer: c) Igneous
Explanation:
Igneous rocks form when magma (below surface) or lava (above surface) cools and solidifies. Examples include granite and basalt.

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3. What is the Mohs scale used to measure?

a) Rock density
b) Mineral hardness
c) Magnetic properties
d) Rock permeability

Answer: b) Mineral hardness
Explanation:
The Mohs scale ranks minerals based on their ability to scratch one another, ranging from talc (1) to diamond (10).


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4. Which layer of the Earth is primarily made of iron and nickel?

a) Crust
b) Mantle
c) Outer core
d) Lithosphere

Answer: c) Outer core
Explanation:
The outer core is primarily composed of liquid iron and nickel, and it is responsible for generating Earth's magnetic field.


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5. What is the name of the boundary between the Earth's crust and mantle?

a) Lithosphere
b) Moho (Mohorovičić discontinuity)
c) Asthenosphere
d) Core

Answer: b) Moho (Mohorovičić discontinuity)
Explanation:
The Moho is the boundary where seismic waves change velocity, marking the transition between the crust and the mantle.


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6. What is the primary agent of weathering?

a) Gravity
b) Water
c) Heat
d) Wind

Answer: b) Water
Explanation:
Water is the most effective agent of weathering, causing both chemical and physical breakdown of rocks through processes like hydrolysis and freeze-thaw.

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7. What is the process of rock transformation due to heat and pressure called?

a) Sedimentation
b) Metamorphism
c) Erosion
d) Lithification

Answer: b) Metamorphism
Explanation:
Metamorphism involves the alteration of rocks in the solid state due to high heat, pressure, or chemically active fluids, forming metamorphic rocks.
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8. Which mineral is the most abundant in the Earth's crust?

a) Quartz
b) Feldspar
c) Mica
d) Calcite

Answer: b) Feldspar
Explanation:
Feldspar minerals make up about 60% of the Earth's crust and are found in igneous, sedimentary, and metamorphic rocks.

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9. What is the term for a naturally occurring, inorganic solid with a specific chemical composition and crystalline structure?

a) Rock
b) Mineral
c) Fossil
d) Ore

Answer: b) Mineral
Explanation:
A mineral is defined by its natural occurrence, inorganic origin, specific chemical composition, and crystalline structure, such as quartz or diamond.

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10. What is plate tectonics?

a) The study of rocks
b) The movement of the Earth's lithospheric plates
c) The process of mineral formation
d) The erosion of rock layers

Answer: b) The movement of the Earth's lithospheric plates
Explanation:
Plate tectonics explains the movement of large lithospheric plates on the Earth's surface, driven by mantle convection, causing earthquakes, volcanoes, and mountain formation.


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11. Which process forms sedimentary rocks?

a) Cooling and solidification
b) Weathering, erosion, deposition, and lithification
c) Heat and pressure
d) Melting

Answer: b) Weathering, erosion, deposition, and lithification
Explanation:
Sedimentary rocks are formed by the accumulation and lithification of sediments derived from weathering and erosion of pre-existing rocks.


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12. What is the name of the supercontinent that existed about 225 million years ago?

a) Gondwana
b) Laurasia
c) Pangaea
d) Rodinia

Answer: c) Pangaea
Explanation:
Pangaea was a supercontinent that existed during the late Paleozoic and early Mesozoic eras, before breaking apart into the continents we see today.


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13. What is the driving force behind volcanic activity?

a) Solar energy
b) Radioactive decay and mantle convection
c) Earth's rotation
d) Magnetic field

Answer: b) Radioactive decay and mantle convection
Explanation:
Volcanic activity is driven by the heat generated from radioactive decay within the Earth's interior and mantle convection processes.


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14. What is a fossil?

a) A mineral deposit
b) Preserved remains or traces of ancient life
c) A type of sedimentary rock
d) A crystal formation

Answer: b) Preserved remains or traces of ancient life
Explanation:
Fossils are the preserved remains, impressions, or traces of organisms that lived in the past, often found in sedimentary rocks.

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15. What is the most common volcanic gas?

a) Methane
b) Carbon dioxide
c) Water vapor
d) Sulfur dioxide

Answer: c) Water vapor
Explanation:
Water vapor is the most abundant gas released during volcanic eruptions, followed by carbon dioxide and sulfur dioxide.

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