Preparation of flocculated suspensions MCQs With Answer

Preparation of flocculated suspensions MCQs with Answer is a vital topic for B. Pharm students. Mastering controlled flocculation, zeta potential, Stokes’ law, sedimentation volume (F), and degree of flocculation (β) helps formulate physically stable suspensions. You will learn how wetting agents, electrolytes, polymers, pH adjustment, and structured vehicles (suspending agents like sodium CMC and xanthan gum) are combined to prevent caking, enhance redispersibility, and ensure dose uniformity. Understanding DLVO theory, bridging flocculation, and desirable rheology (pseudoplastic, thixotropic behavior) supports robust design and evaluation of suspensions using sedimentation rate, sedimentation volume, redispersibility, and zeta potential. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary objective of controlled flocculation in pharmaceutical suspensions?

• To achieve zero sedimentation rate
• To prevent caking while ensuring easy redispersion and dose uniformity
• To increase particle dissolution rate to intravenous levels
• To eliminate the need for wetting agents

Correct Answer: To prevent caking while ensuring easy redispersion and dose uniformity

Q2. Sedimentation volume (F) is defined as:

• F = Vu/Vo
• F = Vo/Vu
• F = V∞/Vu
• F = η/ρ

Correct Answer: F = Vu/Vo

Q3. Degree of flocculation (β) is correctly expressed as:

• β = Vu/V∞
• β = V∞/Vu
• β = F × η
• β = (ρp − ρm)g

Correct Answer: β = Vu/V∞

Q4. According to Stokes’ law, increasing which parameter decreases sedimentation rate?

• Particle radius
• Density difference between particle and medium
• Gravitational acceleration
• Viscosity of the medium

Correct Answer: Viscosity of the medium

Q5. Which class of excipients primarily induces flocculation by reducing zeta potential?

• Electrolytes
• Sweeteners
• Flavoring agents
• Colorants

Correct Answer: Electrolytes

Q6. Bridging flocculation in suspensions is most commonly achieved using:

• Polymers
• Oils
• Sugars
• Volatile solvents

Correct Answer: Polymers

Q7. Which of the following is NOT typically used as a suspending (structured vehicle) agent?

• Sodium carboxymethylcellulose
• Xanthan gum
• Sucrose
• Bentonite

Correct Answer: Sucrose

Q8. The primary role of wetting agents at the start of suspension preparation is to:

• Increase the magnitude of zeta potential
• Reduce interfacial tension and displace air from hydrophobic powders
• Cross-link the polymeric vehicle
• Sterilize the suspension

Correct Answer: Reduce interfacial tension and displace air from hydrophobic powders

Q9. A key characteristic of a deflocculated suspension is:

• Rapid sedimentation with a clear supernatant
• Slow sedimentation but forms a compact cake on standing
• Easily redispersible loose sediment
• High sedimentation volume close to 1

Correct Answer: Slow sedimentation but forms a compact cake on standing

Q10. The most desirable rheological behavior for vehicles in oral flocculated suspensions is:

• Newtonian with high viscosity
• Dilatant behavior
• Pseudoplastic with thixotropy
• Bingham plastic without yield value

Correct Answer: Pseudoplastic with thixotropy

Q11. For negatively charged particles, which electrolyte is most effective at reducing zeta potential and inducing flocculation?

• Aluminum chloride (AlCl3)
• Sodium chloride (NaCl)
• Glucose
• Ethanol

Correct Answer: Aluminum chloride (AlCl3)

Q12. Zeta potential of a suspension is commonly assessed by:

• Potentiometric titration
• Electrophoretic mobility measurement (microelectrophoresis)
• Polarimetry
• Osmometry

Correct Answer: Electrophoretic mobility measurement (microelectrophoresis)

Q13. Adjusting pH during preparation of flocculated suspensions primarily helps to:

• Maximize particle size
• Optimize drug ionization and zeta potential for controlled flocculation
• Eliminate the need for preservatives
• Convert the suspension into an emulsion

Correct Answer: Optimize drug ionization and zeta potential for controlled flocculation

Q14. A sedimentation volume F > 1 in a suspension indicates:

• Presence of deflocculation
• Sediment volume exceeds original volume due to floc swelling/structuring
• Instrument error only
• Phase inversion

Correct Answer: Sediment volume exceeds original volume due to floc swelling/structuring

Q15. Which sequence best represents the key steps in preparing a flocculated suspension?

• Wetting → Dispersion in vehicle → Flocculation → Add structured vehicle → Make up volume/excipients
• Add structured vehicle → Wetting → Make up volume → Flocculation → Dispersion
• Make up volume → Sterilization → Wetting → Flocculation → Packaging
• pH adjustment after bottling → Wetting → Add color → Dispersion → Gelation

Correct Answer: Wetting → Dispersion in vehicle → Flocculation → Add structured vehicle → Make up volume/excipients

Q16. A commonly used wetting agent in oral suspensions is:

• Polysorbate 80 (Tween 80)
• Span 60
• Liquid paraffin
• Talc

Correct Answer: Polysorbate 80 (Tween 80)

Q17. Excessive addition of electrolyte flocculant can:

• Produce a stable microemulsion
• Drive particles into the primary minimum, causing coagulation and poor redispersibility
• Completely stop sedimentation permanently
• Increase zeta potential magnitude

Correct Answer: Drive particles into the primary minimum, causing coagulation and poor redispersibility

Q18. Controlled flocculation improves dose uniformity because:

• Flocs never settle
• Flocs settle rapidly to a porous sediment that redisperse uniformly on shaking
• It sterilizes the product
• It increases osmolarity

Correct Answer: Flocs settle rapidly to a porous sediment that redisperse uniformly on shaking

Q19. Which variable does not appear directly in Stokes’ law for sedimentation rate?

• Particle radius
• Zeta potential
• Density difference (particle–medium)
• Medium viscosity

Correct Answer: Zeta potential

Q20. Which set consists of suitable structured vehicle (suspending) agents for oral suspensions?

• Sodium CMC, xanthan gum, tragacanth
• Sucrose, saccharin, mannitol
• Peppermint oil, ethanol, glycerin
• Sodium chloride, citric acid, sodium benzoate

Correct Answer: Sodium CMC, xanthan gum, tragacanth

Q21. Critical flocculation concentration (CFC) refers to the:

• Highest viscosity attained before gelation
• Electrolyte concentration at which attractive forces exceed repulsion, yielding optimal flocculation
• Concentration where a suspension becomes fully deflocculated
• Amount of polymer needed for wetting

Correct Answer: Electrolyte concentration at which attractive forces exceed repulsion, yielding optimal flocculation

Q22. A convenient practical index for assessing physical stability of flocculated suspensions is:

• Osmolarity measurement
• Sedimentation volume and ease of redispersion over time
• Refractive index
• Drug pKa

Correct Answer: Sedimentation volume and ease of redispersion over time

Q23. A high magnitude of zeta potential (positive or negative) usually indicates:

• Tendency to remain deflocculated due to strong repulsion
• Rapid flocculation
• High thixotropy
• High density

Correct Answer: Tendency to remain deflocculated due to strong repulsion

Q24. Buffer systems are included in flocculated suspensions mainly to:

• Maintain pH to control drug stability and flocculation behavior
• Increase palatability only
• Provide antimicrobial action
• Increase particle density

Correct Answer: Maintain pH to control drug stability and flocculation behavior

Q25. If all other variables are constant, doubling the medium viscosity will:

• Double the sedimentation rate
• Halve the sedimentation rate
• Not change the sedimentation rate
• Cause phase separation

Correct Answer: Halve the sedimentation rate

Q26. In a formulation, the degree of flocculation β = 1.0 implies:

• A highly flocculated system
• No flocculation relative to the deflocculated system
• Severe caking is guaranteed
• F > 1

Correct Answer: No flocculation relative to the deflocculated system

Q27. To prevent caking without excessively increasing viscosity, the best strategy is to:

• Use only very fine particles with no additives
• Induce controlled flocculation and add a pseudoplastic structured vehicle
• Add large amounts of sugar syrup
• Store at high temperature

Correct Answer: Induce controlled flocculation and add a pseudoplastic structured vehicle

Q28. Which polymer can act as a flocculating agent by bridging between particles?

• Polyvinylpyrrolidone (PVP)
• Sodium chloride
• Magnesium stearate
• Citric acid

Correct Answer: Polyvinylpyrrolidone (PVP)

Q29. Why is flocculation typically performed before adding the structured vehicle?

• Because viscosity and polymer adsorption can mask charges and hinder formation of optimal flocs
• To sterilize the product early
• To dissolve the drug first
• To avoid using wetting agents

Correct Answer: Because viscosity and polymer adsorption can mask charges and hinder formation of optimal flocs

Q30. The label “Shake well before use” is critical for flocculated suspensions because:

• Flocculated suspensions sediment rapidly but redisperse to deliver accurate doses
• It prevents evaporation
• It changes pH
• It sterilizes the dose each time

Correct Answer: Flocculated suspensions sediment rapidly but redisperse to deliver accurate doses

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