Fine Solids Dispersion Equipment MCQs With Answer

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

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