Weathering: physical, chemical, and biological

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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.

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.

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

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

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

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

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

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

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

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