Definition and classification of suspensions MCQs With Answer

Suspensions are biphasic pharmaceutical systems where insoluble solid particles are dispersed in a liquid medium. For B.Pharm students, understanding the suspension definition and classification of suspensions is critical for formulation design, stability assessment, and optimizing drug bioavailability. This concise overview covers coarse versus colloidal suspensions, flocculated and deflocculated systems, rheology and sedimentation (Stokes’ law), zeta potential and DLVO concepts, suspending and wetting agents, preservatives, and evaluation parameters such as sedimentation volume, degree of flocculation, redispersibility, and particle size analysis. It also touches on preparation methods and common excipients used to improve stability and dosing accuracy. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary defining characteristic of a pharmaceutical suspension?

• Homogeneous single-phase solution
• Colloidal particles dissolved at molecular level
• Insoluble solid particles dispersed in a liquid medium
• Emulsified oil droplets in water

Correct Answer: Insoluble solid particles dispersed in a liquid medium

Q2. Which classification is based on particle size in suspensions?

• Coarse and fine (colloidal) suspensions
• Flocculated and deflocculated suspensions
• Aqueous and non-aqueous suspensions
• Sterile and non-sterile suspensions

Correct Answer: Coarse and fine (colloidal) suspensions

Q3. Which parameter represents the ratio of the volume of sediment to the original volume of the suspension?

• Degree of flocculation (β)
• Sedimentation volume (F)
• Viscosity index
• Redispersibility index

Correct Answer: Sedimentation volume (F)

Q4. Which law predicts the settling velocity of spherical particles in a suspension?

• Fick’s law
• Stokes’ law
• Henderson-Hasselbalch equation
• Arrhenius equation

Correct Answer: Stokes’ law

Q5. Flocculated suspensions are characterized by which of the following?

• Particles form loose aggregates that settle rapidly but are easily redispersed
• Particles remain as isolated crystals with slow settling
• Particles dissolve to form clear solutions
• Particles form irreversible hard cakes on settling

Correct Answer: Particles form loose aggregates that settle rapidly but are easily redispersed

Q6. Degree of flocculation (β) is defined as:

• The ratio of sedimentation volumes of flocculated to deflocculated suspension
• The difference between initial and final pH of suspension
• The viscosity of suspension divided by water viscosity
• The concentration of preservative needed for stability

Correct Answer: The ratio of sedimentation volumes of flocculated to deflocculated suspension

Q7. Which excipient is primarily used as a suspending agent to increase viscosity?

• Sodium chloride
• Methylcellulose
• Citric acid
• Propylene glycol

Correct Answer: Methylcellulose

Q8. Which is a common wetting agent used to reduce interfacial tension between hydrophobic particles and aqueous medium?

• Sorbitol
• Sodium lauryl sulfate
• Sodium metabisulfite
• Calcium carbonate

Correct Answer: Sodium lauryl sulfate

Q9. Zeta potential is most closely related to which property of suspension particles?

• Magnetic susceptibility
• Surface charge and electrostatic repulsion
• Covalent bonding capacity
• Melting point

Correct Answer: Surface charge and electrostatic repulsion

Q10. DLVO theory explains stability of suspensions by balancing which two forces?

• Hydrophobic and hydrophilic forces
• Van der Waals attraction and electrostatic repulsion
• Gravitational and centrifugal forces
• Viscous and inertial forces

Correct Answer: Van der Waals attraction and electrostatic repulsion

Q11. What is the main goal of adding a dispersing agent in a suspension?

• To increase sedimentation rate
• To prevent aggregation and improve particle separation
• To decrease solubility of drug
• To catalyze chemical degradation

Correct Answer: To prevent aggregation and improve particle separation

Q12. Redispersibility of a sedimented suspension depends primarily on:

• Formation of a hard cake versus loose sediment
• Presence of dissolved drug in medium
• Ambient light intensity
• Volume of packaging

Correct Answer: Formation of a hard cake versus loose sediment

Q13. Which preparation technique reduces particle size by grinding a powder with a small amount of liquid?

• Lyophilization
• Levigation
• Spray drying
• Coacervation

Correct Answer: Levigation

Q14. Ostwald ripening in suspensions refers to:

• Chemical hydrolysis of drug molecules
• Growth of larger particles at expense of smaller ones due to solubility differences
• Rapid flocculation induced by electrolytes
• Evaporation of continuous phase

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

Q15. Which test measures the ease with which a settled suspension can be redispersed?

• pH titration
• Redispersibility test
• IR spectroscopy
• Minimum inhibitory concentration

Correct Answer: Redispersibility test

Q16. Which factor will decrease sedimentation rate according to Stokes’ law?

• Increasing particle diameter
• Decreasing viscosity of medium
• Increasing density difference between particle and medium
• Increasing viscosity of the medium

Correct Answer: Increasing viscosity of the medium

Q17. Which preservative is commonly used in aqueous pharmaceutical suspensions?

• Chloroform
• Benzoic acid or sodium benzoate
• Magnesium stearate
• Sugar syrup

Correct Answer: Benzoic acid or sodium benzoate

Q18. A deflocculated suspension is likely to show which behavior?

• Rapid settling with easy redispersion
• Slow settling and formation of a compact cake
• Immediate dissolution of particles
• Gel formation and no sedimentation

Correct Answer: Slow settling and formation of a compact cake

Q19. Which analytical method is commonly used for particle size determination in suspensions?

• UV-visible spectroscopy
• Laser diffraction
• Titration
• Thin layer chromatography

Correct Answer: Laser diffraction

Q20. Structured vehicles in suspensions (e.g., cellulose derivatives) primarily provide:

• Antibiotic activity
• Viscoelastic network to reduce sedimentation
• Color and flavor enhancement
• High osmolality for injection

Correct Answer: Viscoelastic network to reduce sedimentation

Q21. Which pH-related effect can influence suspension stability?

• pH can alter particle surface charge and zeta potential
• pH controls the particle melting point
• pH determines molecular weight of polymers
• pH prevents physical sedimentation by increasing gravity

Correct Answer: pH can alter particle surface charge and zeta potential

Q22. Which excipient acts as both suspending and wetting agent depending on concentration and chemistry?

• Glycerin
• Polyvinylpyrrolidone (PVP)
• Hydroxypropyl methylcellulose (HPMC)
• Mercury

Correct Answer: Hydroxypropyl methylcellulose (HPMC)

Q23. Which statement about non-aqueous suspensions is true?

• They are always less stable than aqueous suspensions
• They use oils or non-polar solvents as the continuous phase
• They do not require preservatives
• They cannot contain suspending agents

Correct Answer: They use oils or non-polar solvents as the continuous phase

Q24. What is the purpose of using electrolytes in a suspension formulation?

• To increase particle solubility in water
• To modify zeta potential and promote controlled flocculation
• To act as primary suspending polymers
• To sterilize the suspension

Correct Answer: To modify zeta potential and promote controlled flocculation

Q25. Which property best describes a colloidal suspension?

• Particle sizes typically greater than 100 micrometers
• Particles are molecularly dissolved
• Particle sizes range roughly from 1 nm to 1 µm with Brownian motion
• No Brownian motion and immediate sedimentation

Correct Answer: Particle sizes range roughly from 1 nm to 1 µm with Brownian motion

Q26. In evaluating suspension rheology, a pseudoplastic (shear-thinning) behavior is desirable because:

• It increases settling during storage
• It makes suspensions harder to pour
• Viscosity decreases on shaking, easing pouring, and increases at rest to reduce settling
• It prevents drug release

Correct Answer: Viscosity decreases on shaking, easing pouring, and increases at rest to reduce settling

Q27. Which instability phenomenon results from particle aggregation into a tightly packed mass that cannot be redispersed?

• Flocculation
• Caking
• Ostwald ripening
• Crema­tion

Correct Answer: Caking

Q28. Which test helps assess microbial preservation efficacy in suspensions?

• Preservative efficacy test (PET) or antimicrobial effectiveness test
• pH stability test
• Density measurement
• Sediment porosity test

Correct Answer: Preservative efficacy test (PET) or antimicrobial effectiveness test

Q29. Which factor does NOT directly affect the settling rate of particles in a suspension?

• Particle density
• Viscosity of medium
• Particle color
• Particle radius

Correct Answer: Particle color

Q30. For oral pediatric suspensions, which attribute is most critical for patient acceptability and dosing accuracy?

• High turbidity
• Appropriate viscosity, palatability, and uniform redispersibility
• Complete insolubility of drug
• Use of metallic containers only

Correct Answer: Appropriate viscosity, palatability, and uniform redispersibility

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