Weathering: physical, chemical, and biological

Correct answer: C. Water and dissolved substances

Water and dissolved chemicals alter rocks in chemical weathering. Treat water as the main medium in exams.

Correct answer: D. Cracking of rock by tree roots

Tree roots can widen cracks and break rocks. In exams, connect the action of living organisms with biological weathering.

Correct answer: A. Physical weathering

Rocks expand and contract due to temperature, causing breaking. In exams, also relate it to dry regions.

Correct answer: B. Because crystals grow and pressurize cracks

Salt crystals grow in cracks and create pressure. Remember it as a simple example of physical weathering.

Correct answer: C. Chemical weathering

In oxidation, minerals react with oxygen and change. In exams, use rusting of iron as an example.

Correct answer: D. Limestone

Carbonation dissolves calcium-rich rocks like limestone. Remember its link with karst landforms in exams.

Correct answer: A. Water

In hydration, minerals absorb water and may swell. Treat it as a chemical weathering process in exams.

Correct answer: B. Water freezes and expands in cracks

Water freezes and expands in cracks, putting pressure on rocks. Remember freezing and expansion as key words in exams.

Correct answer: D. It helps change rocks into fine particles

Weathering breaks rocks and provides parent material for soil. Link soil formation with weathering in exams.

Correct answer: A. Hot and dry desert region

Deserts have large day-night temperature differences that increase physical breaking. In exams, treat temperature change as the reason.

Correct answer: B. Chemical weathering

In hot and humid conditions, water and heat speed up chemical reactions. Link hot humid climate with chemical weathering in exams.

Correct answer: C. Biological weathering

Biological weathering is the breaking down or weakening of rocks by living organisms. Plant roots are an important biological agent. A small root may enter a crack in a rock. As the plant grows, the root becomes thicker and pushes against the sides of the crack. Repeated growth can widen the crack and eventually split the rock into smaller pieces. This action changes the rock physically, even though the cause is a living organism.

Therefore, choice C, biological weathering, is correct. Carbonation is a chemical process in which carbonic acid in water reacts with certain minerals. Oxidation is another chemical process commonly associated with oxygen and minerals, while evaporation is the change of water into vapour and is not a type of rock weathering in this context. The key clue is the action of tree roots, so connect plants and animals with biological weathering.

Correct answer: D. Exfoliation

In exfoliation, outer layers separate due to pressure or temperature effects. Onion-like layers are a key clue in exams.

Correct answer: A. Chemical weathering

In solution, minerals dissolve in water and change or get removed. In exams, link dissolving with chemical weathering.

Correct answer: B. They loosen soil and help biological weathering

Organisms mix and loosen soil, helping weathering. Write organism activity as biological weathering in exams.

Correct answer: C. Frost weathering

The direct answer is C, Frost weathering. Weathering means breaking or changing rock at or near Earth’s surface without transporting it away. In cold places, water enters a crack, freezes, expands, and pushes the crack walls apart. When it melts, more water can enter. Repeated freezing and thawing gradually widens the crack and breaks the rock into pieces, so this is physical or mechanical weathering. Option A, carbonation, is a chemical reaction in which carbonic acid in water reacts with minerals, especially limestone. Option B, oxidation, is a chemical change often involving oxygen, such as rusting of iron-bearing minerals. Option C is correct because it names the repeated freezing-and-thawing process. Option D, hydration, means minerals take in water and change chemically or expand; it is not the specific process described here. Memory cue: frost means freezing, so frost weathering means ice breaking rock.

Correct answer: D. Oxidation

Direct answer: Option D, oxidation. Chemical weathering changes the minerals within a rock. During oxidation, oxygen reacts with minerals, especially iron-bearing minerals, producing oxides. The result may look reddish or brown, much like rust on iron. Water often helps the reaction, but the key chemical agent named in this question is oxygen. Option A is wrong because exfoliation is mainly a physical process in which outer layers peel away, often due to pressure release or temperature effects. Option B is wrong because frost action is physical weathering caused by freezing and expansion of water in cracks. Option C is wrong because salt crystallization is physical weathering in which growing salt crystals exert pressure. Option D is correct because it directly names the oxygen-mineral reaction. Memory cue: oxygen plus iron gives rust-like oxidation.

Correct answer: A. They allow water and air to enter

Cracks allow water, air, and roots to reach inside the rock. In exams, understand cracks as pathways for weathering.

Correct answer: A. Temperature change

Temperature change makes rocks expand and contract. In exams, choose mechanical breaking causes as physical weathering.

Correct answer: B. Plants and microorganisms

Plants and microorganisms can produce organic acids that weaken rocks. In exams, see it as a mix of biological and chemical effects.

Correct answer: A. Their composition may change

Chemical weathering changes the composition of minerals. In exams, link the word change with chemical process.

Correct answer: B. Physical weathering

Physical weathering breaks rock mechanically. In exams, treat without chemical change as the clue.

Correct answer: C. Chemical weathering

Acidic substances can chemically react with minerals. In exams, connect acid with chemical weathering.

Correct answer: D. Biological or human-induced mechanical breaking

Humans are living agents and can mechanically break rocks. In exams, understand human action under biological influence.

Correct answer: A. Outer surface of rock

Weathering starts from the outer surface and gradually reaches inside. In exams, consider surface contact important.