1 $Soil colloids are generally defined by particle sizes smaller than which of the following?$

A.

B.

C.

D.

2 $Which of the following is not a general property of soil colloids?$

A.

High surface area per unit mass

B.

Surface electric charge

C.

Adsorption of cations and water

D.

Settles rapidly in water

3 $The fundamental building block of silicate clays consisting of one silicon atom surrounded by four oxygen atoms is known as a:$

A.

Silicon Octahedron

B.

Silicon Tetrahedron

C.

Aluminum Octahedron

D.

Magnesium Tetrahedron

4 $Which clay mineral typically has a 1:1 crystal structure?$

A.

Montmorillonite

B.

Illite

C.

Kaolinite

D.

Vermiculite

5 $In a 2:1 type silicate clay, the structure consists of:$

A.

One tetrahedral sheet sandwiched between two octahedral sheets

B.

One octahedral sheet sandwiched between two tetrahedral sheets

C.

Alternating single sheets of silica and alumina

D.

One octahedral sheet and one tetrahedral sheet only

6 $Which phenomenon is primarily responsible for the permanent negative charge found in 2:1 silicate clays?$

A.

pH-dependent dissociation

B.

Protonation of hydroxyl groups

C.

Isomorphous substitution

D.

Broken edges of crystal lattices

7 $Which of the following clay minerals has the highest Cation Exchange Capacity (CEC)?$

A.

Kaolinite

B.

Illite

C.

Vermiculite

D.

Gibbsite

8 $Illite is a non-expanding 2:1 clay primarily because of the fixation of which ion in the interlayer space?$

A.

B.

C.

D.

9 $Which group of soil colloids is amorphous (non-crystalline) and typically found in soils derived from volcanic ash?$

A.

Smectites

B.

Allophane and Imogolite

C.

Iron oxides

D.

Micas

10 $What is the primary source of charge on humus (organic colloids)?$

A.

Isomorphous substitution

B.

pH-dependent dissociation of functional groups

C.

Interlayer fixation

D.

Van der Waals forces

11 $Under highly acidic conditions, the edges of Kaolinite may develop a positive charge due to:$

A.

Protonation

B.

Deprotonation

C.

Isomorphous substitution

D.

Anion repulsion

12 $The Cation Exchange Capacity (CEC) is commonly expressed in which units?$

A.

B.

C.

D.

13 $Which of the following sequences represents the correct order of adsorption strength (Lyotropic series) for cations on clay surfaces?$

A.

B.

C.

D.

14 $The specific surface area of Montmorillonite (Smectite) is significantly higher than Kaolinite because:$

A.

It has only external surface area

B.

It has both internal and external surface area

C.

It is a 1:1 clay

D.

It contains potassium bridges

15 $Which organic matter fraction is soluble in alkali but precipitates when the solution is acidified?$

A.

Fulvic acid

B.

Humic acid

C.

Humin

D.

Lignin

16 $The 'Van Bemmelen factor' used to estimate Soil Organic Matter (SOM) from Soil Organic Carbon (SOC) is approximately:$

A.

1.724

B.

0.58

C.

2.50

D.

1.00

17 $A soil C:N ratio of 50:1 would likely result in which process?$

A.

Net Mineralization of Nitrogen

B.

Net Immobilization of Nitrogen

C.

Immediate release of Nitrate

D.

No biological activity

18 $Which component of plant residues is most resistant to decomposition?$

A.

Sugars

B.

Proteins

C.

Cellulose

D.

Lignin

19 $The process by which individual clay particles stick together to form flake-like aggregates is called:$

A.

Dispersion

B.

Flocculation

C.

Cementation

D.

Leaching

20 $Which cation is the most effective dispersing agent, often leading to poor soil structure?$

A.

B.

C.

D.

21 $Sesquioxides are soil colloids dominated by:$

A.

Silicon and Oxygen

B.

Iron and Aluminum oxides

C.

Potassium and Magnesium

D.

Calcium carbonate

22 $Chlorite is structurally similar to vermiculite but contains an additional sheet in the interlayer space composed of:$

A.

Potassium ions

B.

Water molecules

C.

Magnesium-hydroxide (Brucite-like)

D.

Silica tetrahedrons

23 $The Point of Zero Charge (PZC) is the pH at which:$

A.

The soil has no cations

B.

The net surface charge of the colloid is zero

C.

The soil pH is 7.0

D.

The CEC is maximum

24 $Which fraction of humic substances is soluble in both acid and alkali?$

A.

Humin

B.

Humic acid

C.

Fulvic acid

D.

Hematite

25 $In the octahedral sheet of silicate clays, the central cation is typically:$

A.

or

B.

or

C.

or

D.

or

26 $Which of the following is true regarding the swelling/shrinking capacity of Kaolinite?$

A.

Very high expansion upon wetting

B.

Moderate expansion

C.

Little to no expansion

D.

Expands only in acid soils

27 $The breakdown of organic nitrogen compounds into ammonium () is specifically called:$

A.

Nitrification

B.

Denitrification

C.

Aminization and Ammonification

D.

Immobilization

28 $Which soil colloid typically exhibits the highest specific surface area?$

A.

Kaolinite

B.

Illite

C.

Humus

D.

Fine Sand

29 $Anion Exchange Capacity (AEC) is most likely to be significant in:$

A.

Alkaline soils with 2:1 clays

B.

Highly weathered, acidic soils rich in Fe/Al oxides

C.

Soils high in organic matter only

D.

Saline soils

30 $The ratio of Silicon to Oxygen in a silica tetrahedron is:$

A.

1:2

B.

1:4

C.

2:1

D.

1:6

31 $Which of the following is a crystalline Iron oxide mineral?$

A.

Goethite

B.

Gibbsite

C.

Kaolinite

D.

Quartz

32 $The term 'isomorphous substitution' in tetrahedrons usually involves the substitution of:$

A.

for

B.

for

C.

for

D.

for

33 $Which of the following represents the correct C:N ratio range where neither net mineralization nor net immobilization occurs (equilibrium)?$

A.

10:1 to 15:1

B.

20:1 to 30:1

C.

40:1 to 50:1

D.

> 80:1

34 $Humus enhances soil physical properties primarily by:$

A.

Increasing bulk density

B.

Promoting aggregation and structure stability

C.

Reducing water holding capacity

D.

Increasing soil temperature significantly

35 $The bonding force holding layers of Montmorillonite together is:$

A.

Strong Hydrogen bonds

B.

Potassium bridges

C.

Weak Van der Waals forces

D.

Covalent bonds

36 $Which term describes the process where metal ions are bonded to organic molecules forming a ring structure, increasing metal solubility or availability?$

A.

Precipitation

B.

Chelation

C.

Flocculation

D.

Volatilization

37 $Base Saturation is defined as:$

A.

The percentage of CEC occupied by basic cations ()

B.

The percentage of CEC occupied by acidic cations ()

C.

The total amount of cations in the soil solution

D.

The saturation of soil pores with water

38 $The 'Diffuse Double Layer' theory explains:$

A.

The formation of humus

B.

The distribution of ions near a charged colloid surface

C.

The weathering of feldspar

D.

The decomposition of lignin

39 $Gibbsite is an example of:$

A.

Iron oxide

B.

Aluminum hydroxide

C.

Silicate clay

D.

Organic colloid

40 $Which of the following organic compounds decomposes most rapidly in soil?$

A.

Lignin

B.

Cellulose

C.

Simple sugars and starches

D.

Waxes

41 $The interlayer spacing (c-spacing) of expanded Montmorillonite with water can reach up to:$

A.

0.7 nm

B.

1.0 nm

C.

1.4 nm to > 2.0 nm

D.

0.1 nm

42 $Which clay mineral is most commonly associated with 'cracking' soils (Vertisols)?$

A.

Kaolinite

B.

Smectite/Montmorillonite

C.

Chlorite

D.

Illite

43 $In the context of soil organic matter, 'Active Carbon' refers to:$

A.

The very old, stable humus

B.

The fraction easily utilized by microbes (labile)

C.

Charcoal

D.

Carbonate minerals

44 $What is the primary effect of high sodium saturation on soil colloids?$

A.

Increased flocculation

B.

Dispersion and puddling

C.

Increased aeration

D.

Formation of stable aggregates

45 $The net charge of 1:1 clays like Kaolinite is primarily:$

A.

High permanent negative charge

B.

Low pH-dependent charge

C.

High permanent positive charge

D.

Zero under all conditions

46 $Vermiculite differs primarily from smectite by having:$

A.

Lower CEC

B.

Higher negative charge in the tetrahedral sheet

C.

No isomorphous substitution

D.

A 1:1 structure

47 $Which functional group is most responsible for the acidity of soil organic matter?$

A.

Amino ()

B.

Carboxyl ()

C.

Methyl ()

D.

Aldehyde ()

48 $Colloidal particles in suspension exhibiting random, rapid zigzag motion is a phenomenon known as:$

A.

Tyndall effect

B.

Brownian movement

C.

Osmosis

D.

Diffusion

49 $The total surface area of a soil is dominated by:$

A.

The sand fraction

B.

The silt fraction

C.

The colloidal fraction (clay + humus)

D.

The gravel fraction

50 $In the weathering sequence of clay minerals, which is considered the most weathered (end product)?$

A.

Illite

B.

Vermiculite

C.

Smectite

D.

Sesquioxides (Fe/Al oxides)

Unit 4 - Practice Quiz