Fine Solids Dispersion Equipment MCQs With Answer — Introduction
This collection of MCQs focuses on equipment and principles used for dispersing fine solid particles in liquid media, tailored for M.Pharm students studying MIP 203T – Pharmaceutical Production Technology. It covers common machinery (colloid mills, bead mills, high-pressure homogenizers, rotor–stator mixers, three-roll mills, ultrasonic devices), critical process parameters (shear, cavitation, media selection, tip speed, specific energy), scale-up considerations, contamination and cleaning issues, and formulation aids such as surfactants and zeta potential. These questions are designed to test conceptual understanding and practical decision-making needed for designing and operating dispersion processes in pharmaceutical manufacturing.
Q1. What is the primary mechanism of particle size reduction in a colloid mill?
- High-velocity impact by grinding media
- Shear between rotor and stator
- Cavitation produced by high pressure drop
- Compression between rollers
Correct Answer: Shear between rotor and stator
Q2. Which dispersion equipment uses grinding media to achieve size reduction?
- Colloid mill
- Bead mill (media mill)
- Ultrasonic homogenizer
- Three-roll mill
Correct Answer: Bead mill (media mill)
Q3. Which single factor most strongly influences final particle size in a bead mill?
- Milling media size
- Feed tank temperature
- Rotor blade geometry
- Batch color
Correct Answer: Milling media size
Q4. The predominant mechanisms of dispersion in a high-pressure homogenizer are:
- Thermal conduction and diffusion
- Shear, cavitation and impact through a narrow orifice
- Mechanical compression between rollers
- Magnetic agitation and settling
Correct Answer: Shear, cavitation and impact through a narrow orifice
Q5. For dispersing a heat-sensitive active pharmaceutical ingredient to a coarse suspension, which equipment is most suitable?
- High-pressure homogenizer
- Ultrasonic probe
- High-shear rotor–stator mixer
- Low-shear paddle stirrer
Correct Answer: Low-shear paddle stirrer
Q6. A three-roll mill is especially suitable for processing which type of pharmaceutical material?
- Low-viscosity aqueous suspensions
- High-viscosity pastes, ointments and concentrated dispersions
- Gaseous aerosols
- Frozen dry powders
Correct Answer: High-viscosity pastes, ointments and concentrated dispersions
Q7. To minimize contamination from milling media wear in a bead mill, the most important control is:
- Increasing processing temperature
- Using a wear-resistant, non-contaminating media and efficient separation screen
- Running at maximum possible speed at all times
- Adding abrasive solids to polish the chamber
Correct Answer: Using a wear-resistant, non-contaminating media and efficient separation screen
Q8. Which dispersion technique primarily relies on acoustic cavitation as its working principle?
- Bead milling
- High-pressure homogenization
- Ultrasonic homogenization (sonication)
- Three-roll milling
Correct Answer: Ultrasonic homogenization (sonication)
Q9. In a rotor–stator homogenizer, decreasing the rotor–stator gap size predominantly affects:
- The electrical consumption only
- The degree of shear and resulting particle size
- The color of the dispersion
- The solvent vapor pressure
Correct Answer: The degree of shear and resulting particle size
Q10. When scaling up wet milling processes, a key scalable parameter to preserve is:
- Absolute rotor diameter regardless of speed
- Specific energy input (kWh per unit mass) and tip speed
- Ambient laboratory humidity
- Number of operator interventions
Correct Answer: Specific energy input (kWh per unit mass) and tip speed
Q11. Which formulation factor most directly improves wetting of hydrophobic powders during dispersion?
- Increasing milling time only
- Using surfactants and reducing liquid surface tension
- Reducing impeller diameter
- Adding inert salt to the liquid phase
Correct Answer: Using surfactants and reducing liquid surface tension
Q12. Zeta potential is a measure of:
- Thermal conductivity of the dispersion
- Particle shape and crystallinity
- Electrostatic stability indicating magnitude of repulsive forces
- Viscosity at high shear rates
Correct Answer: Electrostatic stability indicating magnitude of repulsive forces
Q13. The rotor tip speed (U) for a rotating mill rotor is calculated by which relation (N in revolutions per second, D in meters)?
- U = 2 × π × N / D
- U = π × D × N
- U = D / (π × N)
- U = π / (D × N)
Correct Answer: U = π × D × N
Q14. Which equipment is most commonly used for producing nanosuspensions of poorly soluble drugs by media milling?
- Paddle stirrer
- Bead mill (media milling)
- Colloid mill for large solids
- Atmospheric spray dryer
Correct Answer: Bead mill (media milling)
Q15. An advantage of rotor–stator (high-shear) mixers compared to bead mills is:
- They always produce smaller nanoparticle sizes
- Lower contamination risk and higher throughput for coarse to medium dispersions
- They require grinding media to function
- They guarantee sterilization of the product
Correct Answer: Lower contamination risk and higher throughput for coarse to medium dispersions
Q16. A common processing problem observed with high-shear mixing of suspensions is:
- Excessive crystallization due to vacuum
- Air entrainment and foam formation
- Spontaneous polymerization of water
- Loss of pH control due to magnetic fields
Correct Answer: Air entrainment and foam formation
Q17. In continuous bead milling, the residence time of material in the milling chamber is determined by:
- The color of the media
- Chamber volume and flow rate through the mill
- The molecular weight of the API
- The ambient air pressure only
Correct Answer: Chamber volume and flow rate through the mill
Q18. Why are multiple passes (recirculation) through a high-pressure homogenizer often used?
- To increase the solution temperature deliberately
- To progressively reduce particle size and narrow the particle size distribution
- To remove dissolved gases from the solvent
- To sterilize the dispersion by repeated pressure shocks
Correct Answer: To progressively reduce particle size and narrow the particle size distribution
Q19. For forming an oil-in-water nanosuspension, which HLB range of surfactants is generally preferred?
- HLB 1–4
- HLB 4–7
- HLB 8–18
- HLB 20–30
Correct Answer: HLB 8–18
Q20. During cleaning validation of dispersion equipment, hard-to-clean places that require special attention typically include:
- Large flat sight glasses only
- External painted surfaces
- Seals, narrow gaps, screens and milling chamber crevices
- Operator clothing
Correct Answer: Seals, narrow gaps, screens and milling chamber crevices
