1) Soil colloids are important because they: a) Repel all charged ions b) Attract and hold cations due to negative charges c) Only bond with anions d) Reduce soil surface area 2) Soil colloids are generally smaller than: a) 10 mm b) 2 µm c) 50 µm d) 1 cm 3) Which of the following is a 1:1 type clay mineral? a) Smectite b) Vermiculite c) Kaolinite d) Illite 4) The process of replacing one ion with another of similar size in the mineral lattice is called: a) The process of replacing one ion with another of similar size in the mineral lattice is called: b) Weathering c) Isomorphous substitution d) Chelation 5) Permanent negative charge in clay minerals mainly originates from: a) Loss of H⁺ from OH groups b) Isomorphous substitution c) Adsorption of anions d) Root respiration 6) Which clay mineral has the highest CEC? a) Kaolinite b) Smectite c) Iron oxides d) Organic matter 7) Which soil texture generally has the highest CEC? a) Light-colored sand b) Clay and clay loam c) Loam d) Silt loam 8) The cation most strongly adsorbed according to the lyotropic series is: a) Ca²⁺ b) Na⁺ c) K⁺ d) Al³⁺ 9) Anion exchange capacity (AEC) increases when: a) Soil pH increases b) Soil pH decreases c) Temperature increases d) Soil moisture decreases 10) A soil with pH 5 has ______ times more H⁺ ions than pH 7. a) 10 b) 20 c) 100 d) 1000 11) Which form of liming material is known as quicklime? a) CaCO₃ b) CaMg(CO₃)₂ c) CaO d) Ca(OH)₂ 12) Which is a non-expanding clay mineral? a) Smectite b) Vermiculite c) Kaolinite d) Montmorillonite 13) Soil buffering capacity (BC) is highest when the soil contains: a) High sand content b) High clay and organic matter c) Only silt particles d) No exchange sites 14) As soil pH increases, the negative charge on humus generally: a) Decreases b) Increases c) Does not change d) Converts into positive charge 15) Which nutrient moves to plant roots mainly by diffusion? a) Calcium b) Nitrate c) Phosphate d) Sulphate 16) Mass flow is responsible for transporting nutrients due to: a) Water uptake and transpiration b) Root interception c) H⁺ exchange d) Soil compaction 17) Micronutrients (Fe, Mn, Zn, Cu) become more available when soil is: a) Strongly alkaline b) Slightly alkaline c) Neutral d) Acidic 18) The main source of negative charges in 2:1 clays is: a) Carboxyl group b) Phenolic groups c) Isomorphous substitution d) Hydrogen bonding 19) Improving soil structure by liming is a ______ change. a) Biological b) Physical c) Chemical d) Mechanical 20) The movement of ions toward roots due to physical contact between root surfaces and soil particles is called: a) Mass flow b) Diffusion c) Root interception d) Capillary action

AGR231 CHAPTER 6

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