Continuous vs Batch Mixing MCQs With Answer

Continuous vs Batch Mixing MCQs With Answer

Introduction: Continuous and batch mixing are foundational concepts in pharmaceutical production that influence product quality, process control, and regulatory strategy. This quiz collection explores technical differences, mixing theory, scale-up considerations, process analytical technology (PAT), validation, and practical challenges specific to M.Pharm students. Questions emphasize residence time distribution, hydrodynamics, impeller selection, power input, segregation risk, cleaning and CIP, and control strategies for maintaining homogeneity in both continuous and batch systems. The aim is to deepen understanding of when to apply each approach, how to design experiments and scale systems, and how to ensure robust, regulatory-compliant manufacturing of pharmaceutical blends and formulations.

Q1. Which statement best captures the fundamental operational difference between continuous and batch mixing?

• Continuous mixing processes run without interruption and material flows through the system steadily.
• Batch mixing always uses a single impeller type for all formulations.
• Continuous mixing never requires process validation due to constant conditions.
• Batch mixing always yields a superior residence time distribution compared to continuous systems.

Correct Answer: Continuous mixing processes run without interruption and material flows through the system steadily.

Q2. Which residence time distribution (RTD) model commonly represents ideal continuous stirred-tank reactor (CSTR) behavior in mixing?

• Gaussian distribution.
• Exponential distribution.
• Dirac delta distribution.
• Bimodal distribution.

Correct Answer: Exponential distribution.

Q3. For scale-up of a turbulent stirred tank from lab to pilot scale while maintaining geometric similarity, which parameter is typically kept constant?

• Péclet number.
• Power per unit volume (P/V).
• Absolute impeller diameter.
• Batch time.

Correct Answer: Power per unit volume (P/V).

Q4. Which advantage is most associated with continuous mixing compared to batch mixing in pharmaceutical production?

• Lower initial process development complexity and shorter validation time.
• Generally higher throughput with improved steady-state control and smaller footprint.
• Eliminates the need for sampling and in-process controls.
• Requires no cleaning between product changes.

Correct Answer: Generally higher throughput with improved steady-state control and smaller footprint.

Q5. When evaluating blend uniformity in a powder mixing process, which metric directly quantifies relative content variability across samples?

• Residence time.
• Relative Standard Deviation (%RSD).
• Pumping efficiency.
• Power input.

Correct Answer: Relative Standard Deviation (%RSD).

Q6. Which sensor technology is most commonly used as a PAT tool to monitor blend uniformity inline in continuous mixing of powders or granules?

• Nuclear magnetic resonance (NMR).
• Near-infrared spectroscopy (NIR).
• Thermogravimetric analysis (TGA).
• Gas chromatography (GC).

Correct Answer: Near-infrared spectroscopy (NIR).

Q7. In a cascade of continuous stirred tanks intended to approximate plug flow, increasing the number of identical CSTRs in series primarily affects which of the following?

• Decreases total residence time while increasing axial dispersion.
• Approaches plug flow behavior by reducing variance in RTD.
• Makes the RTD more exponential and less sharp.
• Eliminates need for downstream quality control.

Correct Answer: Approaches plug flow behavior by reducing variance in RTD.

Q8. Which mixing phenomenon is most critical to control in high-shear wet granulation processes to ensure consistent granule properties?

• Axial dispersion of gas phases.
• Nucleation and growth kinetics driven by shear and binder distribution.
• Solvent vapor diffusion.
• Electrical conductivity of the granulator shell.

Correct Answer: Nucleation and growth kinetics driven by shear and binder distribution.

Q9. For powder blending, which of the following describes a primary risk when converting a validated batch process into a continuous process without adequate characterization?

• Reduced overall throughput with identical product quality.
• Loss of segregation control and unexpected variability in API concentration.
• Guaranteed decrease in impurity formation.
• Elimination of cross-contamination risk.

Correct Answer: Loss of segregation control and unexpected variability in API concentration.

Q10. Which dimensionless number is most relevant for characterizing the transition between laminar and turbulent mixing regimes in stirred tanks?

• Péclet number.
• Reynolds number.
• Sherwood number.
• Biot number.

Correct Answer: Reynolds number.

Q11. In continuous mixing, achieving steady state is critical. Which parameter indicates that steady state has been reached for concentration of a tracer?

• Concentration at outlet fluctuating randomly.
• Outlet concentration becomes constant versus time within process noise limits.
• Inlet concentration becomes zero.
• Total mass in the system doubles.

Correct Answer: Outlet concentration becomes constant versus time within process noise limits.

Q12. Which cleaning strategy is generally easier to implement and validate for continuous production lines compared to multiple batch vessels?

• Manual disassembly and scrubbing between every production run.
• Closed-loop Clean-In-Place (CIP) systems with validated cycles.
• Using solvents that are not compatible with equipment materials.
• Rinse-only cleaning without validation.

Correct Answer: Closed-loop Clean-In-Place (CIP) systems with validated cycles.

Q13. Which regulatory consideration is most important when shifting from batch to continuous manufacturing for a marketed pharmaceutical?

• No regulatory notification is required if product composition is unchanged.
• Demonstration of process understanding, equivalence or improvement, and potentially post-approval changes submission.
• Elimination of all process validation activities.
• Removing all in-process controls since continuous is self-validating.

Correct Answer: Demonstration of process understanding, equivalence or improvement, and potentially post-approval changes submission.

Q14. Which statement about power number (Np) and its use in scale-up is correct?

• Power number decreases linearly with reactor volume for a given impeller.
• Power number is a function of impeller geometry and is used with Reynolds number to estimate power draw.
• Power number only applies to laminar flow and is irrelevant in turbulent mixing.
• Power number equals Reynolds number at all times.

Correct Answer: Power number is a function of impeller geometry and is used with Reynolds number to estimate power draw.

Q15. When assessing axial mixing in a continuous tubular mixer, which dimensionless group helps quantify the relative importance of convective transport to diffusive transport?

• Prandtl number.
• Péclet number.
• Damköhler number.
• Biot number.

Correct Answer: Péclet number.

Q16. In a batch mixer with multiple impellers on a common shaft, what is the main benefit of using staged impellers rather than a single large impeller?

• They always reduce shear to zero.
• Improve axial mixing and reduce dead zones by distributing flow patterns vertically.
• Make scale-up impossible due to complexity.
• Increase segregation due to competing flows.

Correct Answer: Improve axial mixing and reduce dead zones by distributing flow patterns vertically.

Q17. Which approach is most appropriate to evaluate scale-up risks from benchtop batch mixing to commercial-scale continuous mixing?

• Assume linear scaling of time and use identical impeller tip speed only.
• Conduct dimensional analysis, RTD studies, pilot trials, and PAT implementation to map critical process parameters.
• Skip pilot studies because small-scale data always predict commercial performance.
• Rely solely on vendor-provided performance curves without in-house validation.

Correct Answer: Conduct dimensional analysis, RTD studies, pilot trials, and PAT implementation to map critical process parameters.

Q18. For a continuous powder blending line, which sampling strategy ensures representative monitoring of blend uniformity?

• Single grab sample taken near the inlet only.
• Systematic spatial and temporal sampling across multiple locations and times or inline PAT measurement.
• Only end-of-line QC testing after packaging.
• Random visual inspection of material flow.

Correct Answer: Systematic spatial and temporal sampling across multiple locations and times or inline PAT measurement.

Q19. Which mixing-related failure mode is especially critical for high-potency APIs when moving from batch to continuous processes?

• Improved throughput.
• Containment breach leading to operator exposure and cross-contamination.
• Reduced energy consumption.
• Guaranteed reduction in dust generation.

Correct Answer: Containment breach leading to operator exposure and cross-contamination.

Q20. When comparing mixing time between batch and continuous systems, which statement is true?

• Batch mixing time is irrelevant because continuous systems have infinite mixing time.
• Batch mixing time defines a finite time to reach homogeneity per batch, whereas continuous systems rely on residence time distribution and steady-state operation to achieve homogeneity at the outlet.
• Continuous systems never reach homogeneity due to constant flow.
• Mixing time is identical for both systems if the same impeller is used.

Correct Answer: Batch mixing time defines a finite time to reach homogeneity per batch, whereas continuous systems rely on residence time distribution and steady-state operation to achieve homogeneity at the outlet.

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