Difference between solid and liquid mixing MCQs With Answer

Introduction:
Understanding the difference between solid and liquid mixing is essential for B. Pharm students involved in formulation, process development, and quality control. This guide focuses on solid mixing (powder blending, granulation, segregation) and liquid mixing (suspensions, emulsions, rheology, shear), covering mixing equipment (ribbon blender, V-blender, high-shear mixer, impellers), critical parameters (mixing time, tip speed, Reynolds number, viscosity), and scale-up considerations. Emphasis is on achieving homogeneity, preventing segregation, and ensuring content uniformity for tablets, capsules, suspensions, and emulsions. Practical MCQs reinforce theory, process variables, and QC tests to prepare you for exams and lab work. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary difference between solid mixing and liquid mixing?

• Solid mixing relies mainly on particle movement and segregation control
• Liquid mixing depends solely on evaporation rates
• Solid mixing uses only stirring impellers
• Liquid mixing does not require energy input

Correct Answer: Solid mixing relies mainly on particle movement and segregation control

Q2. Which mixer is commonly used for free-flowing powders to achieve uniform blending?

• High-shear granulator
• V-blender
• Colloid mill
• Rotor-stator homogenizer

Correct Answer: V-blender

Q3. Which parameter is most critical for liquid mixing to overcome viscous resistance?

• Bulk density
• Viscosity
• Angle of repose
• Particle size distribution

Correct Answer: Viscosity

Q4. In powder mixing, segregation refers to:

• The formation of chemical bonds between particles
• The separation of different particle fractions after mixing
• The complete dissolution of powder into solvent
• Improved flowability after blending

Correct Answer: The separation of different particle fractions after mixing

Q5. Which impeller type is suitable for low-viscosity liquid mixing with axial flow?

• Paddle impeller
• Radial turbine
• Propeller impeller
• Anchor impeller

Correct Answer: Propeller impeller

Q6. What is the role of baffles in a stirred tank for liquid mixing?

• Reduce shear stress
• Prevent vortex formation and improve mixing
• Increase evaporation rate
• Lower mixing energy requirement to zero

Correct Answer: Prevent vortex formation and improve mixing

Q7. Which quality test is used to evaluate powder blend uniformity?

• Content uniformity assay
• Tap density only
• pH measurement of powder
• Moisture sorption isotherm only

Correct Answer: Content uniformity assay

Q8. In high-shear wet granulation, what primarily drives agglomeration?

• Electrostatic repulsion
• Liquid binder and shear
• Freeze-drying
• Thermal degradation

Correct Answer: Liquid binder and shear

Q9. For powder mixing, which property increases the tendency to form agglomerates?

• Large particle size and low cohesiveness
• High cohesiveness and small particle size
• Low moisture content and high flowability
• Low surface energy

Correct Answer: High cohesiveness and small particle size

Q10. What dimensionless number characterizes flow regime in liquid mixing?

• Péclet number
• Reynolds number
• Froude number only
• Prandtl number only

Correct Answer: Reynolds number

Q11. Which mixing equipment is preferred for cohesive powders that are hard to blend?

• Mortar and pestle only
• High-shear mixer or granulator
• Static mixer
• Ultrasonic bath

Correct Answer: High-shear mixer or granulator

Q12. What does the term ‘tip speed’ refer to in rotor-based liquid mixers?

• Speed of fluid at vessel wall
• Linear speed at the impeller blade tip
• Rotational speed of the motor shaft only
• Speed of baffles

Correct Answer: Linear speed at the impeller blade tip

Q13. In suspension formulation, which factor improves wetting of hydrophobic particles?

• Use of surfactant or wetting agent
• Reducing temperature drastically
• Adding more powder without liquid
• Increasing particle porosity only

Correct Answer: Use of surfactant or wetting agent

Q14. Which mixer is commonly used for producing emulsions in pharmaceutical formulations?

• Ribbon blender
• High-shear mixer or homogenizer
• V-blender
• Double-cone dryer

Correct Answer: High-shear mixer or homogenizer

Q15. What is the main challenge in scale-up of mixing processes?

• Maintaining identical color of product
• Maintaining similar hydrodynamics and mixing intensity
• Changing formulation composition each time
• Increasing the number of operators

Correct Answer: Maintaining similar hydrodynamics and mixing intensity

Q16. Which parameter indicates how quickly a blend reaches homogeneity?

• Mixing time
• Glass transition temperature
• Burn rate
• Melting point

Correct Answer: Mixing time

Q17. What effect does increasing fill level in a blender typically have on mixing?

• Always decreases mixing efficiency
• Can change blending dynamics; optimal range exists
• Causes immediate chemical reactions
• Has no effect at all

Correct Answer: Can change blending dynamics; optimal range exists

Q18. Which mixing index quantifies the uniformity of a blend?

• Segregation coefficient
• Relative standard deviation (RSD) or variance
• Viscosity index
• Surface tension number

Correct Answer: Relative standard deviation (RSD) or variance

Q19. Which phenomenon is important to consider when mixing powders of different particle sizes?

• Chemical incompatibility only
• Percolation and sifting segregation
• Complete dissolution into each other
• Instant sintering

Correct Answer: Percolation and sifting segregation

Q20. What is the effect of increasing impeller speed in liquid mixing (within laminar to turbulent transition)?

• Decreases power consumption
• Increases shear and mixing intensity
• Has no effect on mass transfer
• Stops circulation completely

Correct Answer: Increases shear and mixing intensity

Q21. Which mixer design minimizes dead zones for viscous liquids?

• Flat-bottom tank without baffles
• Anchor or helical ribbon with proper clearance
• V-blender for solids
• Simple propeller with no contact

Correct Answer: Anchor or helical ribbon with proper clearance

Q22. In solid mixing, what is the role of excipient particle size matching?

• Prevents chemical reaction
• Reduces segregation and improves content uniformity
• Guarantees dissolution enhancement
• Makes granulation unnecessary

Correct Answer: Reduces segregation and improves content uniformity

Q23. Which test helps assess the extent of segregation after blending?

• Segregation stress testing or shake test followed by assay
• FTIR only
• X-ray diffraction only
• pH titration only

Correct Answer: Segregation stress testing or shake test followed by assay

Q24. What is a common reason for poor liquid mixing when using a propeller impeller?

• Too high viscosity causing laminar flow and poor bulk motion
• Excessive aeration always helps
• Using baffles always reduces mixing
• Too low impeller clearance from top only

Correct Answer: Too high viscosity causing laminar flow and poor bulk motion

Q25. Which phenomenon improves mixing by molecular diffusion at small scales?

• Turbulent eddies only
• Molecular diffusion enhanced by shear and turbulence
• Electrostatic attraction only
• Gravitational settling only

Correct Answer: Molecular diffusion enhanced by shear and turbulence

Q26. For achieving uniform distribution of a potent drug in a powder blend, what technique is recommended?

• Direct addition without pre-blending
• Use of ordered mixing or geometric dilution
• Increase humidity to clump powder
• Only milling after tableting

Correct Answer: Use of ordered mixing or geometric dilution

Q27. Which mixer is best for heat-sensitive liquid formulations requiring gentle mixing?

• High-shear rotor-stator at high speed
• Low-shear propeller or paddle with temperature control
• Pulverizer
• V-blender with heating

Correct Answer: Low-shear propeller or paddle with temperature control

Q28. In liquid-solid mixing (suspensions), what determines particle settling rate?

• Stokes’ law factors: particle size, density difference, viscosity
• Only mixing time
• Only color of particles
• Only ambient light

Correct Answer: Stokes’ law factors: particle size, density difference, viscosity

Q29. Which is an advantage of tumble mixers for solids?

• They always generate heat for granulation
• Gentle blending and low shear for fragile particles
• High-shear granulation capability
• Guaranteed elimination of segregation

Correct Answer: Gentle blending and low shear for fragile particles

Q30. What is the primary mixing mechanism in a ribbon blender?

• Axial and radial conveying by inner and outer ribbons
• Vortex-induced turbulence
• Molecular diffusion only
• Electrostatic agitation

Correct Answer: Axial and radial conveying by inner and outer ribbons

Q31. Which property of liquid increases energy required for mixing exponentially?

• Low boiling point
• High viscosity
• Low density only
• Neutral pH only

Correct Answer: High viscosity

Q32. During granulation, what effect does increased binder solution addition have?

• Reduces granule size always
• Promotes granule growth and reduces fines
• Makes powder more hydrophobic
• Completely prevents compaction

Correct Answer: Promotes granule growth and reduces fines

Q33. Which instrument measures viscosity relevant to liquid mixing?

• HPLC
• Viscometer or rheometer
• Particle size analyzer only
• Karl Fischer titrator only

Correct Answer: Viscometer or rheometer

Q34. What is the effect of surfactants in emulsification during mixing?

• Increase interfacial tension to destabilize emulsion
• Lower interfacial tension and stabilize droplets
• Convert liquids into solids instantly
• Eliminate need for mixing

Correct Answer: Lower interfacial tension and stabilize droplets

Q35. Which sampling practice is essential for reliable blend uniformity testing?

• Single sample from top only
• Multiple representative samples from different locations
• Only visual inspection
• Sampling after complete segregation only

Correct Answer: Multiple representative samples from different locations

Q36. What is the common cause of overmixing in powder blends?

• Using too low mixing time always
• Excessive mechanical energy leading to demixing or attrition
• Proper pre-blending only
• Use of baffles in liquids only

Correct Answer: Excessive mechanical energy leading to demixing or attrition

Q37. Which device is effective for inline mixing of two liquid streams without moving parts?

• Static mixer
• Ribbon blender
• V-blender
• Centrifuge

Correct Answer: Static mixer

Q38. In mixing, what does ‘power number’ relate to?

• Ratio of power input to fluid density and impeller speed
• Only the color of the slurry
• Number of baffles in tank only
• pH of the solution

Correct Answer: Ratio of power input to fluid density and impeller speed

Q39. For suspensions, what role do rheology modifiers (thickeners) play during mixing?

• Increase sedimentation rate
• Increase viscosity to reduce settling and improve stability
• Eliminate the need for preservatives only
• Make the suspension volatile

Correct Answer: Increase viscosity to reduce settling and improve stability

Q40. Which mixing strategy helps reduce segregation of fine and coarse particles?

• Mixing at extremely high speed always
• Add fines gradually using ordered mixing with diluent
• Separate particles permanently
• Only compress them into tablets first

Correct Answer: Add fines gradually using ordered mixing with diluent

Q41. Which parameter is directly measured to assess mixing homogeneity in liquids?

• Assay concentration across multiple samples
• Tap density only
• Bulk volume only
• Particle shape only

Correct Answer: Assay concentration across multiple samples

Q42. What is the advantage of high-shear mixers in wet granulation compared to low-shear mixers?

• Produce larger, denser granules with shorter processing time
• Always eliminate the need for drying
• Reduce binder usage to zero
• Are best for volatile solvents only

Correct Answer: Produce larger, denser granules with shorter processing time

Q43. Which phenomenon is leveraged by tumble mixers to achieve blending?

• Intense shear between particles
• Gravity and rotational tumbling causing chaotic motion
• Magnetic attraction of particles
• Electrostatic welding

Correct Answer: Gravity and rotational tumbling causing chaotic motion

Q44. When designing a mixing process, which is a critical consideration for pharmaceutical products?

• Regulatory requirements, content uniformity and degradation limits
• Only the color of the container
• Maximizing noise during operation
• Ignoring cleanability

Correct Answer: Regulatory requirements, content uniformity and degradation limits

Q45. Which statement about emulsions prepared by rotor-stator homogenizers is true?

• They create coarse emulsions only
• They generate high shear to reduce droplet size and create stable emulsions
• They are unsuitable for pharmaceutical use
• They always require heating above boiling point

Correct Answer: They generate high shear to reduce droplet size and create stable emulsions

Q46. What is the consequence of inadequate mixing in tablet formulation?

• Improved dissolution uniformity
• Content uniformity failures and variable potency
• Automatic enhancement of stability
• Better patient compliance always

Correct Answer: Content uniformity failures and variable potency

Q47. Which two properties of powders are most influential on mixing behavior?

• Color and odor
• Particle size distribution and flowability/cohesiveness
• Electrical conductivity only
• Magnetism only

Correct Answer: Particle size distribution and flowability/cohesiveness

Q48. In liquid mixing, what is the effect of temperature on viscosity and mixing?

• Raising temperature typically increases viscosity and reduces mixing
• Raising temperature usually decreases viscosity and can improve mixing
• Temperature has no effect
• Only reduces pH

Correct Answer: Raising temperature usually decreases viscosity and can improve mixing

Q49. What is the primary consideration when selecting a mixing time for powder blends?

• Longest possible time regardless of result
• Achieve homogeneity without overmixing and attrition
• Only operator preference
• Only the cost of blender

Correct Answer: Achieve homogeneity without overmixing and attrition

Q50. Which approach is recommended to evaluate scale-up similarity between lab and production mixers?

• Keep only the motor brand identical
• Use dimensionless numbers (Reynolds, power number) and geometric similarity
• Ignore hydrodynamics and rely on intuition
• Always double the mixing time arbitrarily

Correct Answer: Use dimensionless numbers (Reynolds, power number) and geometric similarity

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com