Weathering: physical, chemical, and biological

The key difference is transport: weathering breaks down or alters rock where it is, whereas erosion removes and transports material. Thus, option A gives the distinction.

Repeated heating and cooling make exposed rocks expand and contract. This can create stress and contribute to cracking, so option B is correct.

Carbon dioxide dissolves in water to form a weak acid, which reacts with and dissolves limestone. This solution process helps form karst features, so option C is correct.

During hydrolysis, water chemically reacts with minerals and changes their composition. Feldspar can be altered into clay minerals such as kaolin, so option D is correct.

Frost action requires water in cracks and repeated freezing and thawing. Freezing water expands and can exert pressure on the crack walls, so option A is correct.

Iron-bearing minerals can react with oxygen to form iron oxides, which commonly give rocks red or brown tones. Therefore, option B is correct.

Joints and fractures expose more rock surface and provide pathways for water and air to enter. This allows weathering to act on more of the rock, so option C is correct.

When overlying pressure is reduced, rock can expand and outer sheets may separate. This sheet-like peeling is called exfoliation, so option D is correct.

Warm conditions generally speed up chemical reactions, and abundant water supports processes such as solution and hydrolysis. Together, these conditions make chemical weathering faster, so option A is correct.

B is correct. Saline water can enter pores and cracks; in dry conditions, evaporation leaves salt crystals behind. As the crystals grow, they exert pressure on the rock and can cause it to break apart.

C is correct. As roots grow into cracks, they can exert pressure and widen them. Root secretions, including organic acids, can also help alter or dissolve minerals, so roots contribute to both physical and biochemical weathering.

D is correct. In jointed rock, corners and edges are exposed to weathering from more sides than flat faces. They therefore tend to weather faster, gradually rounding the blocks into spheroidal forms.

A is correct. Minerals differ in stability and solubility. Minerals that are less stable or more soluble under local conditions generally break down or dissolve faster than more resistant minerals.

B is correct. In hydration, water becomes incorporated into a mineral's structure. The resulting increase in volume can create internal stress, weakening the surrounding rock.

C is correct. In solution weathering, water dissolves minerals that are soluble under the prevailing conditions. The dissolved ions can then be carried away in the water.

D is correct. Weathering breaks down rock to form regolith, which provides mineral material for soil development. Soil formation also involves processes such as the addition and decomposition of organic matter.

B is correct. Organic acids released by lichens and microorganisms can react with minerals, helping to dissolve or alter them. This is a biological contribution to chemical weathering.

C is correct. Carbon dioxide dissolved in water can form weak carbonic acid, which dissolves calcite in limestone. Quartz is generally more resistant to chemical weathering, so calcite-rich rocks can be more susceptible under these conditions.

D is correct. Joints and cracks provide planes of weakness in rock. Physical stresses, such as temperature changes or frost action, can exploit these weaknesses and separate the rock into angular blocks.

The correct answer is B. Carbon dioxide dissolves in rainwater and forms weak carbonic acid. This acidic water can react with and dissolve certain minerals, contributing to chemical weathering.

The correct answer is C. Water entering cracks can chemically dissolve minerals, while the widening of cracks contributes to the physical breakdown of the rock. The example therefore shows the two kinds of weathering working together.

The correct answer is D. Low permeability can restrict water movement into the rock. Since water is involved in many weathering processes, limited infiltration can slow weathering. Grain size alone does not determine the rate.

The correct answer is A. Water expands by about 9% when it freezes into ice. In cracks, this expansion can exert pressure on the surrounding rock and contribute to frost weathering.

The correct answer is B. Weathering processes may act slowly, but their effects can accumulate over long periods and produce substantial changes in rock.

The correct answer is C. Roots can grow into and widen rock cracks, a biological contribution to weathering. In moist conditions, water and organic acids can also react with minerals and chemically alter them.