Settling in suspensions MCQs With Answer

Introduction: Settling in suspensions MCQs With Answer is a focused-review resource for B.Pharm students covering sedimentation, flocculation, deflocculation, Stokes’ law, zeta potential, and the role of suspending agents. This concise, keyword-rich introduction highlights practical formulation concepts such as particle size effects, viscosity control, creaming vs. caking, redispersion, and rheological behavior in liquid suspensions. The questions emphasize both theoretical principles (DLVO theory, Brownian motion, hindered settling) and formulation strategies (electrolytes, surfactants, polymers) to improve your exam readiness and formulation understanding. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What does Stokes’ law describe in the context of suspensions?

• The settling velocity of spherical particles in a viscous fluid under laminar flow
• The dissolution rate of particles in a solvent
• The diffusion coefficient of nanoparticles
• The rate of chemical degradation of suspensions

Correct Answer: The settling velocity of spherical particles in a viscous fluid under laminar flow

Q2. Which factor does NOT directly appear in the classical Stokes’ law expression for sedimentation velocity?

• Particle radius
• Acceleration due to gravity
• Fluid viscosity
• Surface charge (zeta potential)

Correct Answer: Surface charge (zeta potential)

Q3. Sedimentation volume (F) of a suspension is defined as:

• The ratio of the ultimate volume of sediment to the original total volume of suspension
• The total volume of liquid above the sediment
• The time taken for complete sedimentation
• The ratio of initial particle volume to final sediment volume

Correct Answer: The ratio of the ultimate volume of sediment to the original total volume of suspension

Q4. Degree of flocculation (β) is usually calculated by comparing:

• Final sediment volume of flocculated system to that of deflocculated system
• Viscosity before and after flocculation
• Zeta potential before and after addition of electrolyte
• Particle size distribution widths

Correct Answer: Final sediment volume of flocculated system to that of deflocculated system

Q5. Which phenomenon describes upward migration of particles in a suspension when particle density is less than the medium?

• Creaming
• Caking
• Flocculation
• Aggregation

Correct Answer: Creaming

Q6. Which is a desirable rheological property for an oral suspension to resist rapid sedimentation and be easily pourable?

• Pseudoplastic (shear-thinning) with thixotropy
• Newtonian with low viscosity
• Dilatant (shear-thickening)
• Highly elastic gel with no flow

Correct Answer: Pseudoplastic (shear-thinning) with thixotropy

Q7. Flocculated suspensions generally show which of the following compared with deflocculated systems?

• Large loose aggregates that are easily redispersible
• Very compact, irreversibly packed sediment
• Complete molecular dissolution
• No sediment formation

Correct Answer: Large loose aggregates that are easily redispersible

Q8. Which statement about deflocculated suspensions is correct?

• They form a fine sediment that is difficult to redisperse (caking)
• Particles remain as single entities producing slow, compact sediment
• They always exhibit thixotropic behavior
• They are stabilized by flocculating electrolytes

Correct Answer: Particles remain as single entities producing slow, compact sediment

Q9. A zeta potential magnitude above approximately ±30 mV usually indicates:

• Electrostatic stability and tendency to remain dispersed
• Immediate flocculation into large visible flocs
• Strong tendency for caking of sediment
• No effect on suspension stability

Correct Answer: Electrostatic stability and tendency to remain dispersed

Q10. Which of the following is a common suspending agent used to increase viscosity in liquid pharmaceutical suspensions?

• Xanthan gum
• Acetone
• Sodium chloride
• Diethyl ether

Correct Answer: Xanthan gum

Q11. Hindered settling occurs when:

• Particle concentration is high and interactions slow individual settling
• Particles are perfectly spherical and isolated
• The fluid is inviscid and offers no resistance
• The suspension is extremely dilute with no particle interaction

Correct Answer: Particle concentration is high and interactions slow individual settling

Q12. Which of the following reduces sedimentation rate most directly?

• Increasing continuous phase viscosity
• Decreasing fluid viscosity
• Increasing particle density significantly
• Decreasing particle surface area

Correct Answer: Increasing continuous phase viscosity

Q13. Which mechanism best explains reversible flocculation according to DLVO theory?

• Particles are trapped in the secondary minimum of the interaction potential
• Particles merge into a single fused entity in the primary minimum
• Complete electrostatic repulsion prevents any contact
• Van der Waals forces are absent

Correct Answer: Particles are trapped in the secondary minimum of the interaction potential

Q14. Which additive is commonly used as a wetting agent to improve dispersion of hydrophobic powders in aqueous media?

• Sodium lauryl sulfate (surfactant)
• Sucrose
• Magnesium stearate
• Calcium carbonate

Correct Answer: Sodium lauryl sulfate (surfactant)

Q15. Which observation indicates undesirable caking in a suspension?

• Hard, compact sediment that does not redisperse on shaking
• Loose sediment that disperses readily
• Uniform colloidal dispersion with no visible sediment
• Transient creaming that redistributes on gentle shaking

Correct Answer: Hard, compact sediment that does not redisperse on shaking

Q16. Brownian motion is most effective at preventing sedimentation for which particle size range?

• Submicron particles (typically < 1 µm)
• Large particles (> 100 µm)
• Millimeter-sized particles
• Particles larger than 10 µm only

Correct Answer: Submicron particles (typically < 1 µm)

Q17. Which test is commonly used to assess ease of redispersion of a suspension?

• Shake test and observation of time required for uniform dispersion
• pH titration
• Melting point determination
• Viscosity at infinite shear only

Correct Answer: Shake test and observation of time required for uniform dispersion

Q18. Increasing particle size in a suspension generally leads to:

• Increased sedimentation velocity (faster settling)
• Decreased sedimentation velocity (slower settling)
• No change in sedimentation behavior
• Immediate dissolution of particles

Correct Answer: Increased sedimentation velocity (faster settling)

Q19. Which of the following is a function of a flocculating agent?

• Promote formation of loose aggregates that settle rapidly but are redispersible
• Completely dissolve particles into molecular form
• Prevent any particle-particle contact at all
• Create permanent chemical bonding between particles

Correct Answer: Promote formation of loose aggregates that settle rapidly but are redispersible

Q20. Which parameter is most directly increased by adding a polymeric suspending agent like methylcellulose?

• Continuous phase viscosity
• Particle density
• Particle solubility
• Thermal conductivity

Correct Answer: Continuous phase viscosity

Q21. Which statement about sediment porosity and caking is correct?

• Low porosity (tight packing) favors caking and hard sediment
• High porosity always leads to caking
• Caking is independent of porosity
• Porosity only affects color, not caking

Correct Answer: Low porosity (tight packing) favors caking and hard sediment

Q22. Which analytical method measures particle size distribution by light scattering and is applicable to suspensions?

• Laser diffraction
• pH meter
• Thermogravimetric analysis
• Gas chromatography

Correct Answer: Laser diffraction

Q23. Addition of a small concentration of electrolyte to a negatively charged colloidal suspension typically causes:

• Compression of the electrical double layer and enhanced flocculation
• Increase of zeta potential magnitude and stronger repulsion
• Conversion of suspension into molecular solution
• Immediate evaporation of the medium

Correct Answer: Compression of the electrical double layer and enhanced flocculation

Q24. Which property is directly measured by zeta potential analysis?

• Effective surface charge-related potential at the shear plane
• Absolute particle size in nanometers
• Viscosity of the continuous phase
• Sedimentation volume

Correct Answer: Effective surface charge-related potential at the shear plane

Q25. Which formulation strategy can minimize creaming for a low-density dispersed phase?

• Increase the viscosity of the continuous phase
• Decrease continuous phase viscosity
• Decrease particle size to millimeters
• Add volatile organic solvent

Correct Answer: Increase the viscosity of the continuous phase

Q26. Which of the following surfactants can act as both wetting and flocculating agent depending on concentration?

• Tween 80 (polysorbate 80)
• Pure water
• Silica gel
• Hydrochloric acid

Correct Answer: Tween 80 (polysorbate 80)

Q27. In the context of suspensions, what is the primary cause of caking during storage?

• Irreversible consolidation of particles into a closely packed sediment
• Excessive stirring before storage
• Addition of appropriate wetting agents
• Maintaining suspension at low temperature

Correct Answer: Irreversible consolidation of particles into a closely packed sediment

Q28. Which of the following is a typical effect of increasing ionic strength of the medium on colloidal stability?

• Reduced electrostatic repulsion and increased tendency to flocculate
• Increased electrostatic repulsion and improved stability
• Immediate conversion to a gel without sedimentation
• No influence on particle interactions

Correct Answer: Reduced electrostatic repulsion and increased tendency to flocculate

Q29. Which USP-style quality control parameter specifically assesses settling behavior?

• Sedimentation volume or sedimentation rate tests
• Melting point determination
• Optical rotation
• Gas permeability

Correct Answer: Sedimentation volume or sedimentation rate tests

Q30. Which of the following is MOST likely to promote formation of a compact, poorly redispersible sediment?

• Very fine particles with high surface area causing close packing
• Large loosely bound flocs
• High continuous phase viscosity with thickening polymers limiting consolidation
• Use of bridging flocculants only

Correct Answer: Very fine particles with high surface area causing close packing

Q31. Which suspension behavior indicates a desirable balance between settling and redispersibility?

• Rapid settling into loose flocs that are easily redispersed
• No settling at all regardless of shear
• Immediate caking within one hour
• Formation of a rigid, nonflowing gel

Correct Answer: Rapid settling into loose flocs that are easily redispersed

Q32. Which physical property difference between dispersed phase and continuous phase most strongly drives sedimentation?

• Density difference (Δρ) between particle and medium
• Color difference
• Electrical conductivity only
• Magnetic susceptibility only

Correct Answer: Density difference (Δρ) between particle and medium

Q33. Which phenomenon is described by particles becoming trapped in primary minimum of interaction potential?

• Irreversible aggregation (coagulation)
• Reversible flocculation
• Complete stabilization by steric hindrance
• Brownian stabilization

Correct Answer: Irreversible aggregation (coagulation)

Q34. Which suspension type tends to have a higher initial rate of sedimentation but better redisper­sibility?

• Flocculated suspensions
• Deflocculated suspensions
• True solutions
• Gaseous emulsions

Correct Answer: Flocculated suspensions

Q35. Which analytical technique can be used to accelerate sedimentation and assess sediment characteristics quickly?

• Centrifugation
• UV-visible spectroscopy without separation
• Thin layer chromatography
• Polarimetry

Correct Answer: Centrifugation

Q36. Steric stabilization of suspensions is primarily provided by:

• Adsorbed polymers or surfactant layers creating physical barriers
• Increasing ionic strength to compress double layer
• Removing all surfactants from the system
• Heating the suspension to boiling

Correct Answer: Adsorbed polymers or surfactant layers creating physical barriers

Q37. Which parameter is LEAST likely to be improved by increasing viscosity with a polymeric suspending agent?

• Chemical stability of the active drug against hydrolysis
• Sedimentation rate reduction
• Physical stabilization against creaming
• Improved homogeneity during storage (reduced migration)

Correct Answer: Chemical stability of the active drug against hydrolysis

Q38. Which of the following is a common natural suspending agent used historically in pharmacy?

• Acacia (gum arabic)
• Ethyl acetate
• Sodium hydroxide
• Polyvinyl chloride

Correct Answer: Acacia (gum arabic)

Q39. Which term describes the irreversible adhesion of particles to form a hard sediment?

• Caking
• Flocculation
• Creaming
• Redispersion

Correct Answer: Caking

Q40. Which condition would favor flocculation rather than stabilization by electrostatic repulsion?

• Low magnitude zeta potential and presence of neutralizing electrolytes
• High magnitude zeta potential (> ±40 mV)
• Strongly adsorbed steric polymers on particles
• Extremely high continuous phase viscosity only

Correct Answer: Low magnitude zeta potential and presence of neutralizing electrolytes

Q41. What is the effect of temperature increase on viscosity and consequently on sedimentation for most aqueous suspensions?

• Viscosity decreases, leading to faster sedimentation
• Viscosity increases, leading to slower sedimentation
• Temperature has no effect on viscosity
• Viscosity becomes infinite at higher temperature

Correct Answer: Viscosity decreases, leading to faster sedimentation

Q42. Which is a typical role of surfactants in suspension formulations?

• Reduce interfacial tension to improve wetting and dispersion of solids
• Increase particle density drastically
• Make particles chemically unstable
• Convert suspensions into solid tablets directly

Correct Answer: Reduce interfacial tension to improve wetting and dispersion of solids

Q43. In sedimentation theory, Reynolds number must be low for Stokes’ law to apply; low Reynolds number implies:

• Laminar flow around the settling particle
• Turbulent wake behind each particle
• High inertial forces dominating viscous forces
• Particle breakup into smaller pieces

Correct Answer: Laminar flow around the settling particle

Q44. Which parameter quantifies the packing efficiency and void space in a sediment?

• Porosity of the sediment
• Viscosity of suspension
• Zeta potential of particles only
• pH of the medium only

Correct Answer: Porosity of the sediment

Q45. Which of the following is a consequence of Ostwald ripening in suspensions of poorly soluble solids?

• Growth of larger particles at the expense of smaller ones due to solubility differences
• Immediate crystalline dissolution to molecular species
• Spontaneous conversion to a gel phase
• Decrease in mean particle size over time uniformly

Correct Answer: Growth of larger particles at the expense of smaller ones due to solubility differences

Q46. A formulation scientist wants easy redispersibility and minimal visible creaming; which combination is most suitable?

• Moderately viscous medium + controlled flocculation + suitable surfactant
• Extremely low viscosity medium with no surfactant
• Highly deflocculated system with zero viscosity modifiers
• Completely anhydrous vehicle with no liquid

Correct Answer: Moderately viscous medium + controlled flocculation + suitable surfactant

Q47. Which measurement would directly indicate the electrostatic stability of a suspension?

• Zeta potential measurement
• Boiling point elevation
• Optical rotation
• Glass transition temperature

Correct Answer: Zeta potential measurement

Q48. Which of the following methods helps prevent caking by creating a steric barrier around particles?

• Adsorption of nonionic polymers or long-chain surfactants (steric stabilization)
• Removal of all polymers from the formulation
• Drying the suspension to a powder within the container
• Adding high levels of electrolytes to neutralize charges

Correct Answer: Adsorption of nonionic polymers or long-chain surfactants (steric stabilization)

Q49. Which observation suggests that a suspension is deflocculated rather than flocculated?

• Clear supernatant with a compact, hard sediment layer
• Rapid settling into large flocs with turbid supernatant
• No sediment formation even after prolonged standing
• Formation of an elastic gel structure

Correct Answer: Clear supernatant with a compact, hard sediment layer

Q50. For a practical pharmaceutical suspension intended for pediatric use, which formulation goal is most important regarding settling behavior?

• Controlled, rapid settling into loose flocs that re-disperse easily by gentle shaking
• Strong, irreversible caking to ensure long-term stability without shaking
• Maximum creaming to visibly separate phases
• Complete absence of any solid particles

Correct Answer: Controlled, rapid settling into loose flocs that re-disperse easily by gentle shaking

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com