Pseudoplastic systems MCQs With Answer

Pseudoplastic systems MCQs With Answer provide B. Pharm students a focused review of shear‑thinning rheology, formulation design, and practical measurement. This set covers pseudoplastic behavior, flow curves, power‑law models, viscosity–shear rate relationships, polymers and thickeners, thixotropy, instrument selection (Brookfield, capillary), and implications for suspension stability, drug release, and processing. Each question deepens conceptual understanding and analytical skills required for lab practice, quality control, and formulation optimization. Keywords include pseudoplasticity, shear‑thinning, rheology, viscosity, power‑law index, thixotropy, and non‑Newtonian fluids — essential for pharmaceutics courses and exam preparation. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the defining rheological characteristic of a pseudoplastic (shear‑thinning) system?

• Viscosity increases with increasing shear rate
• Viscosity remains constant with shear rate
• Viscosity decreases with increasing shear rate
• Viscosity oscillates with time at constant shear

Correct Answer: Viscosity decreases with increasing shear rate

Q2. Which mathematical model is commonly used to describe pseudoplastic fluids?

• Hagen–Poiseuille equation
• Arrhenius equation
• Ostwald‑de Waele (power‑law) model
• Newtonian linear model

Correct Answer: Ostwald‑de Waele (power‑law) model

Q3. In the power‑law model τ = K·γ̇^n, what does n < 1 indicate?

• Newtonian behavior
• Pseudoplastic (shear‑thinning) behavior
• Dilatant (shear‑thickening) behavior
• Thixotropic time‑dependent behavior

Correct Answer: Pseudoplastic (shear‑thinning) behavior

Q4. Which parameter in the power‑law model represents the consistency index?

• n
• K
• γ̇ (shear rate)
• τ (shear stress)

Correct Answer: K

Q5. Which instrument is most frequently used in formulation labs to measure viscosity of pseudoplastic systems?

• Analytical balance
• Spectrophotometer
• Brookfield rotational viscometer
• Gas chromatograph

Correct Answer: Brookfield rotational viscometer

Q6. Thixotropy differs from pseudoplasticity in that thixotropy is primarily:

• Shear‑thickening and instantaneous
• Time‑dependent shear‑thinning
• Independent of time and shear
• Only observed at very high temperatures

Correct Answer: Time‑dependent shear‑thinning

Q7. Which polymer is commonly used to impart pseudoplastic behavior in suspensions?

• Polyethylene glycol
• Hydroxypropyl methylcellulose (HPMC)
• Sodium chloride
• Potassium bromide

Correct Answer: Hydroxypropyl methylcellulose (HPMC)

Q8. For a pseudoplastic suspension, why is shear‑thinning beneficial during oral administration?

• It increases sedimentation rate
• It reduces flow through syringes and pumps
• It eases swallowing by decreasing viscosity during shear
• It permanently decreases viscosity after first shear

Correct Answer: It eases swallowing by decreasing viscosity during shear

Q9. Which rheogram shape is typical for pseudoplastic fluids?

• Linear straight line through origin
• Curved line with slope decreasing at higher shear rates
• Upward curving line indicating increasing slope
• Horizontal line indicating no shear stress change

Correct Answer: Curved line with slope decreasing at higher shear rates

Q10. If a sample has power‑law index n = 0.4, what is the flow behavior?

• Newtonian
• Dilatant
• Pseudoplastic
• Bingham plastic

Correct Answer: Pseudoplastic

Q11. Which of the following units is appropriate for the consistency index K in the power‑law model?

• Pa·s^n
• mL
• kg
• mol·L^-1

Correct Answer: Pa·s^n

Q12. How does increasing polymer concentration generally affect pseudoplastic suspensions?

• Decreases zero‑shear viscosity
• Increases opacity only
• Increases viscosity and enhances shear‑thinning
• Has no effect on rheology

Correct Answer: Increases viscosity and enhances shear‑thinning

Q13. Which statement about apparent viscosity (ηapp) for pseudoplastic fluids is true?

• ηapp is independent of shear rate
• ηapp increases with increasing shear rate
• ηapp decreases with increasing shear rate
• ηapp equals zero at all shear rates

Correct Answer: ηapp decreases with increasing shear rate

Q14. The hysteresis loop area on an up‑down flow curve indicates:

• Temperature dependence only
• Time‑dependent structural breakdown and recovery (thixotropy)
• Instrument error only
• Newtonian behavior

Correct Answer: Time‑dependent structural breakdown and recovery (thixotropy)

Q15. Which flow behavior is described by a yield value that must be exceeded before flow begins?

• Newtonian fluid
• Pseudoplastic without yield
• Bingham plastic or yield‑stress fluids
• Dilatant fluid

Correct Answer: Bingham plastic or yield‑stress fluids

Q16. Which of the following factors typically decreases viscosity of a pseudoplastic system?

• Increasing polymer molecular weight
• Increasing temperature
• Adding more thickener
• Decreasing shear rate

Correct Answer: Increasing temperature

Q17. In rheology, the term “shear rate” (γ̇) describes:

• The force per unit area applied
• The deformation per unit time (velocity gradient)
• The absolute viscosity at zero shear
• The molecular weight distribution

Correct Answer: The deformation per unit time (velocity gradient)

Q18. Which of these excipients can impart pseudoplasticity to topical gels?

• Sodium chloride alone
• Carbomers (Carbopol)
• Glycerin only
• Magnesium stearate

Correct Answer: Carbomers (Carbopol)

Q19. Which measurement technique provides a controlled shear rate and can be used to derive power‑law parameters?

• Capillary viscometer
• Thermogravimetric analysis
• UV–Vis spectrophotometry
• HPLC

Correct Answer: Capillary viscometer

Q20. Ostwald‑de Waele model is limited when:

• Fluid is perfectly Newtonian
• There is significant yield stress or viscoelasticity
• Shear rate is constant
• Temperature is 25°C

Correct Answer: There is significant yield stress or viscoelasticity

Q21. Which test evaluates stability of a pseudoplastic suspension against sedimentation?

• pH titration only
• Accelerated centrifugation and sedimentation volume measurement
• Gas chromatography
• Flame photometry

Correct Answer: Accelerated centrifugation and sedimentation volume measurement

Q22. A high power‑law K value indicates:

• Low consistency (thin fluid)
• High consistency (thicker fluid)
• Newtonian behavior
• No dependence on shear rate

Correct Answer: High consistency (thicker fluid)

Q23. During formulation, why is the shear‑thinning property advantageous for pumping and mixing?

• It prevents any flow in pumps
• Viscosity increases during pumping which reduces throughput
• Viscosity decreases under shear, easing flow through equipment
• It causes irreversible gelation

Correct Answer: Viscosity decreases under shear, easing flow through equipment

Q24. Which is a typical pharmaceutical example of a pseudoplastic product?

• Water
• Hydrogel topical cream
• Air
• 100% ethanol

Correct Answer: Hydrogel topical cream

Q25. What does a decrease in power‑law index n from 0.8 to 0.3 imply?

• System becomes more Newtonian
• System becomes more shear‑thinning
• System becomes shear‑thickening
• No change in flow behavior

Correct Answer: System becomes more shear‑thinning

Q26. Which cleaning or processing parameter must be considered due to pseudoplasticity?

• Color change at rest
• Shear history affecting viscosity during cleaning
• Electric conductivity only
• pH increase with shear

Correct Answer: Shear history affecting viscosity during cleaning

Q27. Which of the following best describes apparent viscosity in a rotational viscometer measurement?

• True constant viscosity at all shear rates
• Viscosity calculated at the specific applied shear rate
• Viscosity independent of instrument geometry
• Always equal to zero for pseudoplastic fluids

Correct Answer: Viscosity calculated at the specific applied shear rate

Q28. Which phenomenon can mask pseudoplastic behavior in crude measurement?

• Instrument calibration with standards
• Presence of significant yield stress or wall slip
• Using logarithmic plotting
• Measuring at multiple shear rates

Correct Answer: Presence of significant yield stress or wall slip

Q29. In suspension formulation, controlling pseudoplasticity helps primarily to:

• Increase drug crystallinity
• Reduce particle sedimentation and improve pourability
• Change drug chemical structure
• Increase hydrophobicity of APIs

Correct Answer: Reduce particle sedimentation and improve pourability

Q30. Which rheological property is most relevant to syringeability of parenteral gels?

• Optical absorbance
• Shear‑thinning behavior and apparent viscosity at high shear
• Density only
• Thermal conductivity

Correct Answer: Shear‑thinning behavior and apparent viscosity at high shear

Q31. A material that shows increasing viscosity with shear is called:

• Pseudoplastic
• Newtonian
• Dilatant
• Thixotropic

Correct Answer: Dilatant

Q32. Which of the following is TRUE regarding temperature dependence of pseudoplastic systems?

• Viscosity typically increases with temperature
• Viscosity typically decreases with temperature
• Power‑law index n always increases with temperature
• Temperature has no effect on rheology

Correct Answer: Viscosity typically decreases with temperature

Q33. Which laboratory practice ensures reliable rheological data for pseudoplastic samples?

• Ignoring sample history and measuring immediately
• Pre‑shearing or standardizing shear history before measurement
• Measuring only at a single shear rate
• Using uncalibrated instruments

Correct Answer: Pre‑shearing or standardizing shear history before measurement

Q34. Herschel–Bulkley model differs from power‑law by including:

• Temperature coefficient
• Yield stress term
• Viscosity at infinite shear
• Solubility parameter

Correct Answer: Yield stress term

Q35. Which approach helps reduce thixotropic breakdown while maintaining pseudoplasticity?

• Increasing shear rate during storage
• Selecting polymers with stronger network recovery (e.g., crosslinked carbomers)
• Reducing polymer molecular weight drastically
• Heating sample above degradation temperature

Correct Answer: Selecting polymers with stronger network recovery (e.g., crosslinked carbomers)

Q36. Which parameter would you report to compare shear‑thinning of two formulations?

• Density only
• Power‑law index n and consistency K
• pH only
• Melting point

Correct Answer: Power‑law index n and consistency K

Q37. What is the effect of dispersed particle loading on pseudoplastic suspensions?

• Little effect on rheology
• Typically increases viscosity and may enhance shear‑thinning
• Always makes system Newtonian
• Always makes system gaseous

Correct Answer: Typically increases viscosity and may enhance shear‑thinning

Q38. Which of the following is NOT a cause of apparent shear‑thinning in measurements?

• True molecular orientation under shear
• Particle alignment or breakup of aggregates
• Instrument wall slip leading to lower measured torque
• Increase in molecular weight during shear

Correct Answer: Increase in molecular weight during shear

Q39. When designing ophthalmic suspensions, why is controlled pseudoplasticity important?

• To ensure rapid ocular drainage
• To provide low viscosity at blink shear and higher viscosity at rest for retention
• To permanently gel after application
• To increase particulate sedimentation rate

Correct Answer: To provide low viscosity at blink shear and higher viscosity at rest for retention

Q40. The term “apparent yield stress” in a pseudoplastic formulation refers to:

• Always zero for pseudoplastic systems
• An observed stress below which negligible flow occurs due to structure
• The stress when the sample boils
• The electrical conductivity threshold

Correct Answer: An observed stress below which negligible flow occurs due to structure

Q41. Which phenomenon is likely if a pseudoplastic gel shows large hysteresis on repeated shear cycles?

• High elastic recovery and immediate restructuring
• Significant thixotropic breakdown and slow recovery
• Perfectly reversible Newtonian flow
• No structural change at any time

Correct Answer: Significant thixotropic breakdown and slow recovery

Q42. In formulation QC, which test complements rheological profiling for pseudoplastic systems?

• Microbial limit test only
• Sedimentation volume and redispersion time
• Atomic absorption spectroscopy
• Karl Fischer titration exclusively

Correct Answer: Sedimentation volume and redispersion time

Q43. Which change indicates stronger shear‑thinning behavior when comparing two rheograms?

• Smaller decrease in viscosity with shear
• Greater decrease in viscosity with increasing shear rate
• Linear increase in shear stress with shear rate
• No change in slope across shear rates

Correct Answer: Greater decrease in viscosity with increasing shear rate

Q44. Which surfactant effect might modify pseudoplastic behavior in emulsions?

• Changing interfacial film strength and droplet interactions
• Only affecting color
• Reducing molecular weight of polymer
• Making continuous phase gaseous

Correct Answer: Changing interfacial film strength and droplet interactions

Q45. For quality control, which reporting practice is essential for rheological data?

• Omitting shear rate or geometry details
• Reporting shear‑rate range, temperature, instrument geometry and pre‑shear history
• Reporting only the product name
• Only reporting visual appearance

Correct Answer: Reporting shear‑rate range, temperature, instrument geometry and pre‑shear history

Q46. Which molecular interaction primarily contributes to network formation in pseudoplastic gels?

• Covalent degradation under shear
• Physical entanglements, hydrogen bonding and ionic interactions
• Radioactive decay
• None — networks do not form in gels

Correct Answer: Physical entanglements, hydrogen bonding and ionic interactions

Q47. How does electrolyte addition often affect polyelectrolyte‑stabilized pseudoplastic systems?

• Has no effect on rheology
• Can screen charges and cause network collapse or flocculation, altering viscosity
• Always makes system Newtonian
• Eliminates all viscosity

Correct Answer: Can screen charges and cause network collapse or flocculation, altering viscosity

Q48. Which formulation goal can be achieved by tuning pseudoplasticity in oral suspensions?

• Reducing taste masking
• Balancing pourability with sedimentation control
• Converting API to gas
• Making suspension non‑sterile

Correct Answer: Balancing pourability with sedimentation control

Q49. When interpreting power‑law parameters, which combination indicates a very viscous, strongly shear‑thinning sample?

• Low K, n > 1
• High K, n ≈ 1.5
• High K, n < 0.5
• Zero K, n = 0

Correct Answer: High K, n < 0.5

Q50. For accelerated stability testing of pseudoplastic formulations, which condition is NOT typically assessed?

• Temperature cycling
• Freeze‑thaw cycles if relevant
• Exposure to shear history and agitation
• Exposure to gamma radiation at manufacturing sterilization doses without justification

Correct Answer: Exposure to gamma radiation at manufacturing sterilization doses without justification

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