GPAT & Pharmacist Recruitment (AIIMS, ESIC, Railways, HSSC)-level MCQs on suspensions: sedimentation, flocculation, and stability.

Q1. In a pharmaceutical suspension, reducing particle size always improves physical stability.

A. True, because the sedimentation rate decreases
B. False, because it may increase caking tendency
C. True, because Brownian motion dominates
D. False, because viscosity decreases

Answer: B
Trap: Smaller particles decrease sedimentation rate but increase compact pack formation, resulting in caking risk.

Q2. Which condition MOST invalidates the application of Stokes’ law in suspensions?

A. Low particle size
B. Dilute system
C. High particle concentration
D. Spherical particles

Answer: C
Trap: Stokes’ law assumes free independent settling, which violates concentrated systems.

Q3. Sedimentation rate is directly proportional to the following:

A. 1/viscosity
B. Particle diameter
C. (Density of medium − density of particle)
D. Temperature only

Answer: A
Trap: The correct relation is rate ∝ (directly proportional to) d² (not d) and ∝ (directly proportional to) (ρp − ρm). Where ρ = density, ρρ = density of particles, ρm = density of medium

Q4. A suspension shows very slow sedimentation but forms a hard cake. This indicates:

A. Flocculated system
B. Deflocculated system
C. Controlled flocculation
D. High-viscosity system

Answer: B
Concept trap: Slow settling results in a hard cake, meaning a deflocculated system.

Q5. Which modification will NOT reduce sedimentation rate?

A. Increasing viscosity
B. Reducing particle size
C. Increasing density difference
D. Increasing structured vehicle

Answer: C
Trap: Increasing the density difference actually increases sedimentation.

Q6. Which statement is TRUE regarding flocculated suspensions?

A. Sedimentation is slow and compact
B. Redispersibility is poor
C. Sediment volume is large
D. Zeta potential is high

Answer: C
Concept: Flocs: loose, bulky sediment, mean high sedimentation volume.

Q7. Flocculation occurs

A. Repulsive forces dominate
B. Attractive forces slightly exceed repulsive forces
C. Zeta potential is maximum
D. Particle size becomes molecular

Answer: B
Trap: Moderate attraction mean floc formation

Q8. Which system is MOST prone to caking?

A. Flocculation in suspension
B. Deflocculation in suspension
C. Controlled flocculation in suspension
D. Vehicle system, Structured

Answer: B
Concept: Close packing indicates irreversible cake formation.

Q 9. Sedimentation volume (F) is 1, indicating:

A. A complete sedimentation
B. An ideal flocculated system
C. Deflocculation in suspension
D. No sedimentation at all

Answer: B
Trap: F = 1: no clear supernatant: ideal system

Q10. The definition of the degree of flocculation (β) is:

A. F∞ / F
B. F / F∞
C. V₀ / Vᵤ
D. V∞ / V₀

Answer: B
Concept: β compares the flocculated vs deflocculated state.

Q11. An ideal suspension characteristic:

A. No sedimentation
B. A high sedimentation rate
C. Settle down slowly but redispersible easily
D. Zero viscosity

Answer: C
Concept: Practical stability means easy redispersion

Q12. Which system gives the best dose uniformity during storage?

A. Deflocculation
B. Flocculation
C. Controlled flocculation
D. High viscousity

Answer: C
Trap: Combines the advantages of both systems

Q13. Increasing viscosity improves stability by:

A. Reducing zeta potential
B. Decreasing sedimentation rate
C. Preventing flocculation
D. Increasing density

Answer: B
Concept: Sedimentation ∝ (is directly proportional to) 1/viscosity

Q14. Which factor primarily controls the transition between flocculated and deflocculated systems?

A. Particle size
B. Zeta potential
C. Density
D. Temperature

Concept: Electrostatic repulsion vs. attraction balance
Q15. Controlled flocculation is achieved mainly by:

A. Reduced viscosity
B. Increased particle size
C. Adjusted zeta potential using electrolytes
D. Removed suspending agents

Answer: C
Concept: Electrolytes reduce zeta potential for floc formation.

Q16.

Assertion (A): Flocculated suspensions settle faster than deflocculated ones.
Reason (R): Flocs behave as larger particles.

A. Both true, R correct explanation
B. Both are true; R is not an explanation.
C. A true, R false
D. A false, R true

Answer: A

Q17.

Assertion (A): Deflocculated suspensions are more stable.
Reason (R): They show a slow sedimentation rate.

Answer: C
Trap: Slow sedimentation does not mean stability due to caking

Q18.

Assertion (A): Increase in particle size improves stability.
Reason (R): Decrease in sedimentation rate.

Answer: D
(Both are false)

Q19.

Assertion (A): High zeta potential can prevent flocculation.
Reason (R): It increases particles' repulsive forces.

Answer: A

Q20.

Assertion (A): Brownian motion prevents sedimentation in suspension.
Reason (R): It is significant only for very small particles.

Answer: A

Q21. Which system appears most elegant but is pharmaceutically inferior?

A. Flocculated
B. Deflocculated
C. Controlled flocculated
D. Structured

Answer: B
Trap: Flocculation looks uniform, but forms a cake

Q22. A suspension with F > 1 indicates the following:

A. Error in Measurement
B. Deflocculation
C. Flocculated system with swelling
D. No sedimentation at all

Answer: C

Q23. Which BEST reflects redispersibility?

A. Its Sedimentation rate
B. Its sedimentation volume
C. Its degree of flocculation
D. Its particle density

Answer: C

Q24. Which will MOST effectively prevent caking?

A. Reducing viscosity
B. Inducing controlled flocculation
C. Increasing particle size
D. Increasing density difference

Answer: B

Q25. In suspension stability, the system

A. is thermodynamically stable
B. is thermodynamically unstable but kinetically stable
C. is in a completely unstable
D. is always in an equilibrium system

Answer: B

Dr. Alok Singh