1. During soil acidification (decrease in pH), which ion primarily replaces calcium (Ca²⁺) on soil cation exchange sites?

 Chloride (Cl⁻)

 Sodium (Na⁺)

 Hydrogen (H⁺)

 Potassium (K⁺)

2. In acidic soils (pH < 5.5), which of the following plant nutrients becomes less available?

 Manganese (Mn)

 Iron (Fe)

 Molybdenum (Mo)

 Zinc (Zn)

3. Low soil pH (<5.5) increases the solubility and availability of _______

 Potassium (K⁺)

 Magnesium (Mg²⁺)

 Calcium (Ca²⁺)

 Aluminum (Al³⁺)

4. ________________ the process that primarily removes calcium (Ca²⁺) from the root zone in humid region soils

 Leaching

 Precipitation

 Fixation

 Adsorption

5. The availability of boron (B) to plants in most mineral soils generally _______ with increasing soil pH

 Increases

 Remains constant

 Decreases

 Becomes toxic regardless of concentration

6. High buffering capacity (resistance to pH change) is associated with _______

 High clay content and high soil organic matter

 Sandy soils

 Low soil organic matter

 Low cation exchange capacity

7. A decrease in soil pH from 7.0 to 5.0 indicates a _______

 20-fold increase in acidity

 2-fold increase in acidity

 100-fold increase in acidity

 1000-fold increase in acidity

8. In soil organic matter and clay minerals, protonation of functional groups (e.g., –COO⁻, –O⁻) results in _______

 Increased alkalinity of the surrounding solution

 No change in surface charge

 Reduction in negative charge

 More negative charge on the surface

9. In soil chemistry, active acidity refers to _______

 H⁺ bound to clay surfaces

 Al³⁺ held on cation exchange sites

 Total soil acidity

 H⁺ present in the soil solution

10. Specific adsorption of phosphate onto Fe/Al oxides occurs via _______

 Ligand exchange

 Precipitation as FePO₄

 Outer-sphere electrostatic attraction

 Cation bridging

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