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?
(a) Both Statement-II and Statement-III are correct and both of them explain Statement-I
(b) Both Statement-II and Statement-III are correct, but only one of them explains Statement-I
(c) Only one of the Statements II and III is correct and that explains Statement-I
(d) Neither Statement-II nor Statement-III is correct

Correct Answer: (a) Both Statement-II and Statement-III are correct and both of them explain Statement-I

Statement-I: Rainfall is one of the reasons for weathering of rocks.
- This statement is true. Rainfall contributes to the weathering process through both physical and chemical means.
Statement-II: Rain water contains carbon dioxide in solution.
- This statement is true. Rainwater absorbs carbon dioxide from the atmosphere, forming a weak carbonic acid solution, which can chemically weather rocks.
Statement-III: Rain water contains atmospheric oxygen.
- This statement is true. Rainwater contains dissolved oxygen from the atmosphere, which can participate in oxidation processes that contribute to weathering.

Option Analysis:

Option (a): Both Statement-II and Statement-III are correct and both of them explain Statement-I.
- This option is correct. Both carbon dioxide and atmospheric oxygen in rainwater contribute to the chemical weathering of rocks.
Option (b): Both Statement-II and Statement-III are correct, but only one of them explains Statement-I.
- This option is incorrect. Both statements II and III are accurate and relevant to explaining weathering processes.
Option (c): Only one of the Statements II and III is correct and that explains Statement-I.
- This option is incorrect. Both statements are correct and contribute to the weathering process.
Option (d): Neither Statement-II nor Statement-III is correct.
- This option is incorrect. Both statements are accurate descriptions of the components of rainwater and their roles in weathering.

Learn More

Weathering: The breaking down or dissolution of rocks and minerals on the Earth’s surface.
- Types of Weathering:
  - Physical (Mechanical) Weathering:
    - Involves the breakdown of rocks and minerals by physical forces such as temperature changes, freeze-thaw cycles, and biological activity.
    - Example: Freeze-thaw action where water seeps into cracks, freezes, expands, and breaks the rock apart.
  - Chemical Weathering:
    - Involves the breakdown of rocks and minerals through chemical reactions, often involving water, acids, and gases.
    - Carbonation: Rainwater containing dissolved CO2 forms carbonic acid, which reacts with minerals like calcite in limestone, leading to dissolution.
    - Oxidation: Oxygen in rainwater reacts with minerals, particularly iron-bearing ones, to form oxides or rust, leading to weakening and breakdown.
    - Hydrolysis: Water reacts with minerals to form new minerals and soluble salts, altering the rock structure.
- Factors Influencing Weathering:
  - Climate: Temperature and precipitation are critical; warm, wet climates enhance chemical weathering, while cold climates promote physical weathering.
  - Rock Type: Different minerals weather at different rates; for example, feldspar weathers faster than quartz.
  - Topography: Slope steepness affects the exposure of rocks to weathering agents.
  - Biological Activity: Plants, microbes, and animals contribute to both physical and chemical weathering through root growth, organic acids, and physical disturbances.
- Importance of Weathering:
  - Soil Formation: Weathering is essential for breaking down rocks into smaller particles that mix with organic material to form soil.
  - Nutrient Cycling: Releases essential minerals and nutrients into the soil, making them available for plant uptake.
  - Landscape Shaping: Influences the formation of various landforms and contributes to the geological cycle.