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Q7 (IAS/2024) Geography › World Physical Geography › Weathering and erosion Official Key

Consider the following statements : Statement-I : Rainfall is one of the reasons for weathering of rocks. Statement-II : Rain water contains carbon dioxide in solution. Statement-III : Rain water contains atmospheric oxygen. Which one of the following is correct in respect of the above statements ?

Result
Your answer: —  ·  Correct: A
Explanation

The correct answer is option A because both Statement-II and Statement-III are factually correct and both explain how rainfall causes weathering of rocks.

Rainfall is naturally acidic with a pH of ~5.6 as CO2 dissolves in the rainwater producing weak carbonic acid[1]. Rain-water contains enough carbon dioxide to make it a weak acid, and solution is the most potent weathering process in limestone regions because the rain-water attacks and dissolves the calcium carbonate[2]. This confirms Statement-II is correct and explains Statement-I.

Chemical weathering processes including solution, carbonation, hydration, oxidation and reduction act on rocks, and water and air (oxygen and carbon dioxide) along with heat must be present to speed up all chemical reactions[3]. Oxidation is the reaction of oxygen in air or water with minerals in the rock, for example, iron in rocks when in contact with air is changed to iron oxide[4]. This confirms Statement-III is correct and also explains Statement-I.

Since both statements are correct and both independently explain how rainfall causes weathering (through carbonation and oxidation respectively), option A is the correct answer.

Sources
  1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 6: Geomorphic Movements > Anthropogenic Solution Weathering > p. 91
  2. [2] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > CHEMICAL WEATHERING > p. 36
  3. [3] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Chemical Weathering Processes > p. 40
  4. [4] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > CHEMICAL WEATHERING > p. 37
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Q. Consider the following statements : Statement-I : Rainfall is one of the reasons for weathering of rocks. Statement-II : Rain water c…
At a glance
Origin: From standard books Fairness: High fairness Books / CA: 10/10 · 0/10

A classic 'Sitter' derived straight from the fundamentals of Chemical Weathering. It rewards aspirants who didn't just memorize landforms but understood the chemical equations (Oxidation and Carbonation) behind them. If you read NCERT Class XI Geomorphic Processes or GC Leong Ch 4, this was unmissable.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
Is rainfall a cause of the weathering of rocks?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > CHEMICAL WEATHERING > p. 36
Presence: 5/5
“But much of the weathered material, or regolith (remains of the rock), may stay in position forming the basis of soil. Regolith is simply the mineral remains of decomposed rocks, but soil contains organic materials, such as the roots of plants; fallen leaves, small animals such as worms, bacteria and so on. When a soil cover exists, chemical weathering of the underlying rocks does not cease; on the contrary it is usually enhanced. This is because the soil absorbs rain-water and keeps the underlying rocks in contact with this moisture. The rain-water absorbs organic acids from the soil and thus becomes a stronger weathering agent than pure rain-water acting on bare rock.”
Why this source?
  • States that soil absorbs rain-water and keeps underlying rock moist, enhancing chemical weathering
  • Notes rain-water picks up organic acids in soil and becomes a stronger agent of rock decomposition
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Physical Weathering Processes > p. 41
Presence: 4/5
“forces could be: (i) gravitational forces such as overburden pressure, load and shearing stress; (ii) expansion forces due to temperature changes, crystal growth or animal activity; (iii) water pressures controlled by wetting and drying cycles. Many of these forces are applied both at the surface and within different earth materials leading to rock fracture. Most of the physical weathering processes are caused by thermal expansion and pressure release. These processes are small and slow but can cause great damage to the rocks because of continued fatigue the rocks suffer due to repetition of contraction and expansion.”
Why this source?
  • Identifies water pressures from wetting and drying cycles as a force that fractures rock
  • Links repeated moisture-driven expansion/contraction to physical weathering and rock fatigue
Science-Class VII . NCERT(Revised ed 2025) > Chapter 5: Changes Around Us: Physical and Chemical > 5.7.1 Weathering of rocks > p. 67
Presence: 4/5
“The red colour is a result of the iron oxide produced when the rock surface was exposed for a long time to water or air containing water vapour. These physical and chemical changes in rocks are collectively called weathering, which eventually leads to the formation of soil.”
Why this source?
  • Describes exposure to water or moist air producing chemical changes (e.g., iron oxide) in rock
  • Classifies those physical and chemical changes caused by water exposure collectively as weathering
Statement 2
Does rainwater contain dissolved carbon dioxide (CO2) from the atmosphere?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 6: Geomorphic Movements > Carbonation – Natural Solution Weathering > p. 90
Presence: 5/5
“• Carbonation refers to reactions of carbon dioxide to give carbonates, bicarbonates, and carbonic acid.• Carbonation weathering is a process in which atmospheric carbon dioxide leads to solution weathering. As rain falls, it dissolves small amounts of carbon dioxide from the air, forming a weak acid that can dissolve some minerals like limestone (calcium carbonate) (solution weathering).• When carbonic acid reacts with limestone, it produces calcium bicarbonate, partially soluble in water (dissolution weathering).• Caves are formed when underground water containing carbonic acid travels through blocks of limestone, dissolves out the limestone, and leaves empty pockets (caves) behind (E.g. Karst topography).• Carbonation process speeds up with a decrease in temperature because colder water holds more dissolved carbon dioxide gas.”
Why this source?
  • Explicitly states that as rain falls it dissolves small amounts of atmospheric CO2, forming a weak acid (carbonic acid).
  • Directly links dissolved CO2 in rainwater to carbonation (solution weathering) of minerals like limestone, showing functional presence.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 6: Geomorphic Movements > Anthropogenic Solution Weathering > p. 91
Presence: 5/5
“• Rainfall is naturally acidic ― pH of ~5.6 (CO2 dissolves in the rainwater producing weak carbonic acid). • Sulphur dioxide, SO2, comes from volcanic eruptions or fossil fuels. The conversion of metallic ores to pure metals often results in the formation of sulphur dioxide.”
Why this source?
  • States rainfall is naturally acidic (pH ~5.6) and attributes this acidity to CO2 dissolving in rainwater to produce weak carbonic acid.
  • Provides a quantitative pH context that supports the chemical effect of dissolved atmospheric CO2 in rain.
Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > CHEMICAL WEATHERING > p. 36
Presence: 5/5
“There are three major chemical weathering processes. l. Solution. Many minerals are dissolved by water, especially when, as with rain-water, it contains enough carbon dioxide to make it a weak acid. Solution is the most potent weathering process in limestone regions because the rain-water attacks and dissolves the calcium carbonate of which the rock is chiefly formed. The dissolved calcium carbonate is”
Why this source?
  • Notes many minerals are dissolved by water particularly when rainwater contains enough CO2 to make it a weak acid, linking CO2 presence to solution weathering.
  • Reinforces that dissolved atmospheric CO2 in rain enhances the solvent power of rainwater for carbonate rocks.
Statement 3
Does dissolved carbon dioxide in rainwater form carbonic acid that chemically weathers rocks?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 6: Geomorphic Movements > Carbonation – Natural Solution Weathering > p. 90
Presence: 5/5
“• Carbonation refers to reactions of carbon dioxide to give carbonates, bicarbonates, and carbonic acid.• Carbonation weathering is a process in which atmospheric carbon dioxide leads to solution weathering. As rain falls, it dissolves small amounts of carbon dioxide from the air, forming a weak acid that can dissolve some minerals like limestone (calcium carbonate) (solution weathering).• When carbonic acid reacts with limestone, it produces calcium bicarbonate, partially soluble in water (dissolution weathering).• Caves are formed when underground water containing carbonic acid travels through blocks of limestone, dissolves out the limestone, and leaves empty pockets (caves) behind (E.g. Karst topography).• Carbonation process speeds up with a decrease in temperature because colder water holds more dissolved carbon dioxide gas.”
Why this source?
  • Defines carbonation as reactions of CO2 producing carbonates, bicarbonates and carbonic acid.
  • Explicitly states rainwater dissolves atmospheric CO2 to form a weak acid that can dissolve minerals such as limestone (solution weathering).
  • Links this process to dissolution features (e.g., cave/karst formation), showing geological effect.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 17: Major Landforms and Cycle of Erosion > Chemistry Behind Karst Landforms > p. 227
Presence: 5/5
“• In its pure state, limestone is made up of calcium carbonate, but where magnesium is also present, it is termed dolomite. Limestone is an organically formed sedimentary rock (formed by the decomposition of calcareous shells) and is soluble in rainwater. The carbonic acid that causes karstic features is formed as rain passes through the atmosphere picking up carbon dioxide. Once the rain reaches the ground, it may pass through soil that can provide much more carbon dioxide to form a weak carbonic acid solution, which dissolves calcium carbonate (limestone).”
Why this source?
  • States carbonic acid is formed as rain picks up CO2 and additional CO2 from soil, creating a weak carbonic solution.
  • Directly asserts this weak carbonic acid dissolves calcium carbonate (limestone), producing karstic features.
Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Activity 2.5 > p. 21
Presence: 5/5
“On passing excess carbon dioxide the following reaction takes place: CaCO s 3 Ca(HCO aq 3 ( )+ H O(l)+ CO (g) → ) ( ) 2 2 2 (Soluble in water) Limestone, chalk and marble are different forms of calcium carbonate. All metal carbonates and hydrogencarbonates react with acids to give a corresponding salt, carbon dioxide and water. Thus, the reaction can be summarised as – Metal carbonate/Metal hydrogencarbonate + Acid → Salt + Carbon dioxide + Water”
Why this source?
  • Gives the chemical reaction converting CaCO3 + CO2 + H2O into soluble calcium bicarbonate, demonstrating the dissolution mechanism.
  • Summarises that metal carbonates/hydrogencarbonates react with acids to yield soluble products, CO2 and water.
Statement 4
Does rainwater contain dissolved atmospheric oxygen (O2)?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 9: The Amazing World of Solutes, Solvents, and Solutions > What inspired Asima Chatterjee to work on medicinal plants? > p. 139
Presence: 5/5
“Chapter 9 — The Amazing World of Solutes, Solvents, and Solutions 139 9.3 Solubility of Gases Many gases, including oxygen, dissolve in water. Oxygen dissolves in water only to a small extent. Even though present in minute quantities, it is this dissolved oxygen that sustains all aquatic life, including plants, fishes, and other organisms. Is the mixture of gases in water a uniform or non-uniform mixture? It is a uniform mixture because the gases dissolve evenly in water to form a solution. Does temperature affect the solubility of gases in liquids also? If so, how? It has been observed that the solubility of gases generally decreases as temperature increases.”
Why this source?
  • Explicitly asserts that many gases, including oxygen, dissolve in water.
  • Specifies oxygen dissolves to a small extent, implying its presence in aqueous phases.
  • Connects dissolved oxygen to sustaining aquatic life, showing functional relevance of dissolved O2.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 6: Geomorphic Movements > Anthropogenic Solution Weathering > p. 91
Presence: 4/5
“• Rainfall is naturally acidic ― pH of ~5.6 (CO2 dissolves in the rainwater producing weak carbonic acid). • Sulphur dioxide, SO2, comes from volcanic eruptions or fossil fuels. The conversion of metallic ores to pure metals often results in the formation of sulphur dioxide.”
Why this source?
  • States that CO2 dissolves in rainwater to form weak carbonic acid, demonstrating that rainwater dissolves atmospheric gases.
  • Provides a direct example of gas uptake by rainwater, supporting the general principle that O2 from the atmosphere can dissolve into rain.
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > b) Sulphur Cycle > p. 21
Presence: 4/5
“Atmospheric hydrogen sulphide also gets oxidised into sulphur dioxide. Atmospheric sulphur dioxide is carried back to the earth after being dissolved in rainwater as weak sulphuric acid. Whatever the source, sulphur in the form of suiphates is take up by plants and incorporated through a series of metabolic processes into sulphur bearing amino acid which is incorporated in the proteins of autotroph tissues. It then passes through the grazing food chain. Sulphur bound in living organism is carried back to the soil, to the bottom of ponds and lakes and seas through excretion and decomposition of dead organic material. The Bio-geochemical cycles discussed here are only a few of the many cycles present in the ecosystem.”
Why this source?
  • Describes atmospheric SO2 being carried back to earth after dissolving in rainwater as weak sulphuric acid.
  • Offers an additional instance of atmospheric gases dissolving in rainwater, reinforcing that rainwater can contain dissolved gases including O2.
Statement 5
Does dissolved atmospheric oxygen in rainwater contribute to the weathering of rocks through oxidation?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > CHEMICAL WEATHERING > p. 37
Presence: 5/5
“In jointed rocks, temperature change cracks up rectangular blocks. Warm wet climates promote rapid chemical weathering, while dry climates inhibit chemical weathering. Dry climates, however, provide good conditions for physical or mechanical weathering. 2. Oxidation. Oxidation is the reaction of oxygen in air or water with minerals in the rock. For example, most rocks contain a certain amount of iron, which when it comes in contact with air is changed to iron oxide, familiar brownish crust or rust. Iron oxide crumbles easily and is far more easily eroded than the original iron. It is thus removed, loosening the overall structure of the rocks and weakening them.”
Why this source?
  • Explicitly defines oxidation as reaction of oxygen in air or water with rock minerals
  • Gives iron → iron oxide (rust) example showing oxygen in water/air causes mineral breakdown
  • Links formation of iron oxides to weakening and increased erosion of rocks
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 6: Geomorphic Movements > Oxidation and Reduction > p. 91
Presence: 4/5
“• In weathering, oxidation means a combination of a mineral with oxygen to form oxides (rusting in the case of iron) or hydroxides. Red soils appear red due to the presence of iron oxides. Oxidation occurs when there is ready access to the atmosphere and water. The minerals most involved in this process are iron, manganese, sulphur etc.• When oxidised minerals are placed in an environment where oxygen is absent, reduction occurs. Such conditions usually exist below the water table, in stagnant water and on waterlogged ground. The red colour of iron upon reduction turns to greenish or bluish grey.”
Why this source?
  • Describes oxidation as combination of a mineral with oxygen to form oxides/hydroxides
  • States oxidation occurs where there is ready access to the atmosphere and water (i.e., oxygen + water present)
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Chemical Weathering Processes > p. 40
Presence: 4/5
“A group of weathering processes viz; solution, carbonation, hydration, oxidation and reduction act on the rocks to decompose, dissolve or reduce them to a fine clastic state through chemical reactions by oxygen, surface and/or soil water and other acids. Water and air (oxygen and carbon dioxide) along with heat must be present to speed up all chemical reactions. Over and above the carbon dioxide present in the air, decomposition of plants and animals increases the quantity of carbon dioxide underground. These chemical reactions on various minerals are very much similar to the chemical reactions in a laboratory.”
Why this source?
  • Lists oxygen (with surface/soil water) as an agent driving chemical weathering processes
  • Notes that presence of water and oxygen speeds up chemical reactions involved in weathering
Pattern takeaway: UPSC Geography is shifting from 'Location-based' to 'Process-based'. They are testing the scientific principles (chemistry/physics) underlying geographical phenomena. You must know *how* a rock breaks, not just *that* it breaks.
How you should have studied
  1. [THE VERDICT]: Sitter. Direct hit from NCERT Class XI (Fundamentals of Physical Geography), Chapter 6: Geomorphic Processes and GC Leong Chapter 4.
  2. [THE CONCEPTUAL TRIGGER]: Chemical Weathering mechanisms. Specifically, identifying the active agents (Water, Oxygen, Carbon Dioxide) and their corresponding processes (Solution, Oxidation, Carbonation).
  3. [THE HORIZONTAL EXPANSION]: Memorize the 'Big 5' Chemical Weathering types: 1. Solution (Solubility), 2. Carbonation (CO2 + Water = Carbonic Acid vs Limestone), 3. Hydration (Water absorption e.g., Anhydrite to Gypsum), 4. Oxidation (Rusting of Iron), 5. Hydrolysis (H+ ions turning Feldspar to Clay).
  4. [THE STRATEGIC METACOGNITION]: Don't just read 'Weathering breaks rocks'. Ask 'What is the chemical reaction?'. The question simply converted two basic chemical equations into English sentences: (H2O + CO2 → Carbonic Acid) and (Fe + O2 + H2O → Rust).
Concept hooks from this question
📌 Adjacent topic to master
S1
👉 Rainwater as a chemical weathering agent
💡 The insight

Rainwater interacting with soil and rock promotes chemical reactions that decompose minerals.

High-yield for questions on weathering mechanisms and soil formation; links geomorphology with hydrology and pedology. Enables answers explaining why humid regions have faster chemical breakdown and soil development.

📚 Reading List :
  • Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > CHEMICAL WEATHERING > p. 36
  • Science-Class VII . NCERT(Revised ed 2025) > Chapter 5: Changes Around Us: Physical and Chemical > 5.7.1 Weathering of rocks > p. 67
🔗 Anchor: "Is rainfall a cause of the weathering of rocks?"
📌 Adjacent topic to master
S1
👉 Wetting–drying cycles and water pressure in physical weathering
💡 The insight

Repeated wetting and drying produces water pressures and expansion/contraction that fracture rocks.

Useful for distinguishing mechanical vs chemical weathering processes and for explaining episodic rock breakdown (e.g., in monsoon climates). Connects to landslides, rockfalls and mass movement topics frequently tested.

📚 Reading List :
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Physical Weathering Processes > p. 41
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 6: Geomorphic Movements > Landslides in India > p. 89
🔗 Anchor: "Is rainfall a cause of the weathering of rocks?"
📌 Adjacent topic to master
S1
👉 Climate control on rates and types of weathering
💡 The insight

Warm, wet climates accelerate chemical weathering while dry climates favour mechanical weathering.

Core concept for linking climate zones to landscape evolution, erosion patterns and soil profiles; helps answer comparative questions about regional geomorphology and environmental adaptation.

📚 Reading List :
  • Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > CHEMICAL WEATHERING > p. 37
  • Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 7: Arid or Desert Landforms > The Mechanics of Arid Erosion > p. 69
🔗 Anchor: "Is rainfall a cause of the weathering of rocks?"
📌 Adjacent topic to master
S2
👉 Carbonation (solution weathering)
💡 The insight

Carbonation describes CO2 dissolving in water to form carbonic acid which dissolves carbonate minerals such as limestone.

High-yield for physical geography and geomorphology questions; explains karst and cave formation, links chemical weathering to rock-cycle and landform evolution, and helps answer questions on weathering mechanisms and landscape change.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 6: Geomorphic Movements > Carbonation – Natural Solution Weathering > p. 90
  • Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > CHEMICAL WEATHERING > p. 36
🔗 Anchor: "Does rainwater contain dissolved carbon dioxide (CO2) from the atmosphere?"
📌 Adjacent topic to master
S2
👉 Acidic nature of natural rainwater (pH ≈ 5.6)
💡 The insight

Rainwater attains slight acidity because dissolved atmospheric CO2 forms weak carbonic acid, giving a characteristic pH around 5.6.

Important for environmental chemistry and atmospheric studies; distinguishes natural acidity from anthropogenic acid rain and connects to impacts on soils, vegetation, and built structures—useful for questions on pollution vs natural processes.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 6: Geomorphic Movements > Anthropogenic Solution Weathering > p. 91
  • Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > CHEMICAL WEATHERING > p. 36
🔗 Anchor: "Does rainwater contain dissolved carbon dioxide (CO2) from the atmosphere?"
📌 Adjacent topic to master
S2
👉 CO2 dissolution and early hydrosphere formation
💡 The insight

Dissolution of atmospheric CO2 in rainwater contributed to removal of CO2 from the atmosphere and to formation/chemistry of early oceans.

Useful for questions on Earth's early atmosphere and ocean formation; links planetary evolution, the carbon cycle, and long-term sequestration processes—helps tackle comparative planetology and geochemical cycle questions.

📚 Reading List :
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 2: The Origin and Evolution of the Earth > Evolution of Atmosphere and Hydrosphere > p. 16
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 3: Geological Time Scale The Evolution of The Earths Surface > 3. Geological Time Scale – The Evolution of The Earth's Surface > p. 43
🔗 Anchor: "Does rainwater contain dissolved carbon dioxide (CO2) from the atmosphere?"
📌 Adjacent topic to master
S3
👉 Carbonation (carbonic acid) weathering
💡 The insight

Dissolved CO2 in water produces weak carbonic acid that chemically dissolves carbonate rocks such as limestone.

High-yield for physical geography questions on chemical weathering and landform development (karst, caves). Connects weathering processes to rock types and landscape evolution, useful for explaining formation of solutional landforms and human–environment interactions.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 6: Geomorphic Movements > Carbonation – Natural Solution Weathering > p. 90
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 17: Major Landforms and Cycle of Erosion > Chemistry Behind Karst Landforms > p. 227
🔗 Anchor: "Does dissolved carbon dioxide in rainwater form carbonic acid that chemically we..."
🌑 The Hidden Trap

Hydrolysis of Feldspar. While Carbonation weathers Limestone, Hydrolysis is the primary enemy of Granite (turning Feldspar into Kaolin Clay). Expect a future statement: 'Hydrolysis is the main weathering process in granitic terrains of humid tropics.'

⚡ Elimination Cheat Code

The 'Universal Solvent' Logic. Water in nature is never pure H2O; it interacts with the atmosphere. Since the atmosphere contains CO2 and O2, rain *must* contain them. If rocks rust (oxidation) or dissolve (limestone), these dissolved gases are the only logical culprits. The science is circular and self-evident.

🔗 Mains Connection

Environment & Climate Change (Enhanced Weathering). The weathering of silicate rocks consumes atmospheric CO2 (The Walker Thermostat). This is a natural carbon sink. In Mains, link this to 'Enhanced Rock Weathering' as a Geo-engineering solution for Carbon Sequestration.

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SIMILAR QUESTIONS

NDA-I · 2014 · Q65 Relevance score: 3.05

Statement I: Chemical weathering processes are found more active in hot and humid environment. Statement II: High temperature and rainfall help in the process of decomposition of rocks.

NDA-II · 2013 · Q31 Relevance score: 2.33

Statement I : The process of decay and disintegration of rocks in situ is called weathering. Statement I : Weathering takes place both mechanically and chemically.

IAS · 2023 · Q63 Relevance score: 2.22

Consider the following statements : Statement-I : The soil in tropical rain forests is rich in nutrients. Statement-II : The high temperature and moisture of tropical rain forests cause dead organic matter in the soil to decompose quickly. Which one of the following is correct in respect of the above statements?

IAS · 2025 · Q28 Relevance score: 1.94

Consider the following statements : Statement I : In the context of effect of water on rocks, chalk is known as a very permeable rock whereas clay is known as quite an impermeable or least permeable rock. Statement II : Chalk is porous and hence can absorb water. Statement III : Clay is not at all porous. Which one of the following is correct in respect of the above statements?

IAS · 2023 · Q64 Relevance score: 1.10

Consider the following statements : Statement-I : The temperature contrast between continents and oceans is greater during summer than in winter. Statement-II : The specific heat of water is more than that of land surface. Which one of the following is correct in respect of the above statements?