Weathering: physical, chemical, and biological

Frost action works when water in cracks freezes, expands, and breaks rock. For exams, remember fluctuating temperature around freezing point.

In spheroidal weathering, corners and edges decay faster because of greater exposed surface area. Link it with chemical weathering in jointed rocks.

Evaporation allows salt crystals to grow and widen cracks. In exams, call it salt weathering or crystallisation pressure.

In carbonation, carbonic acid dissolves calcite and affects limestone. Remember its link with karst landforms in exams.

Hydrolysis can alter silicate minerals into clay minerals. For exams, remember feldspar changing into clay such as kaolin.

Iron-bearing minerals develop rust-like colours through oxidation. In exams, connect it with reddish-yellow soil colours.

Hydration may cause volume change, while hydrolysis alters mineral structure. Treat both as separate chemical processes in exams.

Lichens support biochemical weathering. In exams, use them as an example of vegetation assisting chemical breakdown.

Greater permeability allows water and air to enter the rock. Connect it with both chemical and physical weathering in exams.

Less stable minerals are more vulnerable to chemical weathering. In exams, treat mineral composition as a major control of weathering rate.

When overlying load is removed, rock expands and may break into sheets. Call it pressure-release physical weathering in exams.

Heat and moisture accelerate chemical reactions. In exams, consider warm humid regions ideal for chemical weathering.

Direct answer: Option A, dry regions with a large day-night temperature range. Thermal expansion and contraction are physical weathering processes. During the hot day, the outer part of a rock expands. During the cool night, it contracts. Repeated unequal expansion and contraction create stress, especially near the surface. Cracks may grow, and thin outer layers can eventually break away. Dry regions often have strong sunshine and a large daily temperature range, so option A is the best choice. Option B is less suitable because nearly constant temperature on the sea floor produces little repeated thermal stress. Option C is less suitable because permanent ice keeps temperature changes limited and hides the rock from direct daily heating. Option D is wrong because marshes with very little temperature difference do not provide strong repeated expansion and contraction. The process is physical, not chemical: the mineral composition need not change. Memory cue: hot day, cool night, repeated stress—think dry desert thermal weathering.

Weathering occurs in place, while erosion removes material. In exams, write the difference as in-situ breakdown versus transport.

Iron-bearing minerals react with oxygen and water to form coloured oxides. Remember products like hematite and limonite in exams.

Direct answer: Option A, soluble minerals such as rock salt and gypsum. Solution weathering occurs when water dissolves minerals directly. The rate is especially high where the material is readily soluble and water can reach it repeatedly. Rock salt is a very clear example, and gypsum is also relatively soluble compared with resistant minerals. Option A is therefore correct. Option B is wrong because quartz is hard and generally resistant to direct dissolution under ordinary surface conditions. Option C is not the best answer because dry ash has little available water, and the wording does not identify a readily soluble mineral undergoing solution. Option D is wrong because a completely waterproof metal does not allow water to dissolve it in the way described. Solution is different from physical breaking: the material enters the water as dissolved chemical matter. Memory cue: if the question says solution weathering, look first for salt, gypsum, limestone and water; among these options, salt and gypsum give the clearest answer.

Clay minerals swell with water and shrink on drying. Connect this with physical weathering and soil cracks in exams.

Roots grow into cracks and apply mechanical pressure. In exams, treat it as physical breakage by a biological agent.

Cutting and mining expose fresh surfaces to air and water. In exams, write human activity as a factor increasing weathering rate.

Weathering provides mineral matter and fine particles for soil. In exams, treat weathering as the first stage of soil formation.

Joints allow weathering agents to penetrate into rock. In exams, write structure as an important control of weathering.

In lateritic weathering, leaching removes silica and may leave iron-aluminium residues. Link it with warm humid regions in exams.

Carbonic acid dissolves calcite and enlarges underground cavities. In exams, treat karst as a major example of chemical weathering.

Quartz is generally more stable, while feldspar can chemically alter. Remember the idea of mineral stability order in exams.

Repeated freezing and thawing are necessary for frost weathering. In exams, distinguish permanent cold from repeated crossing of freezing point.