Surfactants and co-solvency methods MCQs With Answer

Introduction:

This collection of MCQs on Surfactants and Co-solvency Methods is designed for M.Pharm students preparing for examinations and practical applications in product development and technology transfer. Questions cover fundamental concepts such as critical micelle concentration (CMC), hydrophilic–lipophilic balance (HLB), micelle structure, cloud point and phase inversion, as well as practical aspects of co-solvents, hydrotropes and scale-up challenges. Emphasis is placed on mechanistic understanding, analytical methods to determine surfactant behavior, formulation implications for solubility and stability, and regulatory/toxicity considerations. These items aim to deepen conceptual knowledge and support confident decision-making during formulation design and technology transfer.

Q1. Which of the following best describes the primary function of a surfactant in pharmaceutical formulations?

• Increase solution viscosity to stabilize suspensions
• Reduce interfacial and surface tension to enhance wetting and emulsification
• Act as a buffering agent to control pH
• Chelate metal ions to prevent oxidation

Correct Answer: Reduce interfacial and surface tension to enhance wetting and emulsification

Q2. What does the critical micelle concentration (CMC) represent?

• The maximum concentration of surfactant soluble in water
• The concentration at which surfactant molecules begin to form micelles
• The concentration giving the highest viscosity in solution
• The surfactant concentration where pH is neutralized

Correct Answer: The concentration at which surfactant molecules begin to form micelles

Q3. The Hydrophilic–Lipophilic Balance (HLB) number is primarily used to:

• Predict the molecular weight of a surfactant
• Estimate the tendency of a surfactant to form o/w or w/o emulsions
• Measure the toxicity of a surfactant
• Determine the CMC of a surfactant

Correct Answer: Estimate the tendency of a surfactant to form o/w or w/o emulsions

Q4. Which class of surfactant is generally preferred for stabilizing oil-in-water (o/w) emulsions in parenteral and topical formulations?

• Cationic surfactants with low HLB
• Nonionic surfactants with high HLB (e.g., Tween 80)
• Anionic surfactants with very low molecular weight
• Zwitterionic surfactants with negative HLB

Correct Answer: Nonionic surfactants with high HLB (e.g., Tween 80)

Q5. How does increasing ionic strength (adding electrolyte) typically affect the CMC of ionic surfactants?

• It increases CMC markedly for all ionic surfactants
• It decreases CMC by screening headgroup repulsion
• It converts ionic surfactants into nonionic surfactants
• It has no effect on CMC of ionic surfactants

Correct Answer: It decreases CMC by screening headgroup repulsion

Q6. Hydrotropy differs from classical co-solvency in that a hydrotrope:

• Is a large nonpolar solvent that dissolves drug in oil phase
• Is a small, highly water-soluble organic compound that increases aqueous solubility of sparingly soluble drugs
• Always forms micelles like surfactants
• Is used only to adjust pH for solubility

Correct Answer: Is a small, highly water-soluble organic compound that increases aqueous solubility of sparingly soluble drugs

Q7. Which mechanism best explains how classical co-solvents (e.g., ethanol, PEG 400) increase solubility of lipophilic drugs in aqueous media?

• They chemically react with the drug to form more soluble salts
• They lower the dielectric constant and reduce water structure, increasing drug solubility in the mixed solvent
• They form covalent complexes with the drug
• They increase the CMC of all surfactants present

Correct Answer: They lower the dielectric constant and reduce water structure, increasing drug solubility in the mixed solvent

Q8. Which physical property of the aqueous phase is most directly reduced by adding common organic co-solvents such as ethanol or propylene glycol?

• Vapor pressure
• Dielectric constant
• Boiling point elevation
• Surface tension of pure water only

Correct Answer: Dielectric constant

Q9. Which experimental technique is most commonly used to determine the CMC of nonionic surfactants based on abrupt changes in surface properties?

• Ultraviolet-visible spectroscopy (UV-Vis)
• Surface tensiometry (surface tension measurements)
• Gel permeation chromatography (GPC)
• Atomic absorption spectroscopy (AAS)

Correct Answer: Surface tensiometry (surface tension measurements)

Q10. The Phase Inversion Temperature (PIT) technique for emulsion preparation relies on which property of nonionic ethoxylated surfactants?

• Their permanent ionization at all temperatures
• The temperature-dependent change in hydrophilicity leading to transient phase inversion
• Their ability to polymerize at high temperature
• Their photochemical instability under ambient light

Correct Answer: The temperature-dependent change in hydrophilicity leading to transient phase inversion

Q11. What does the cloud point of a nonionic surfactant solution indicate?

• The pH at which surfactant ionizes
• The temperature above which the solution becomes turbid due to phase separation of surfactant-rich and water-rich phases
• The concentration at which micelles first form
• The maximum viscosity achievable by the surfactant solution

Correct Answer: The temperature above which the solution becomes turbid due to phase separation of surfactant-rich and water-rich phases

Q12. Which of the following is a typical cosolvent used to enhance the aqueous solubility of poorly water-soluble drugs?

• Sodium lauryl sulfate only
• Ethanol, propylene glycol or polyethylene glycol 400
• Hydrochloric acid at high concentration
• Pure vegetable oil

Correct Answer: Ethanol, propylene glycol or polyethylene glycol 400

Q13. How does adding a co-solvent generally affect the apparent partition coefficient (P) of a lipophilic drug between octanol and water?

• Co-solvent increases aqueous drug solubility, decreasing the apparent partition coefficient
• Co-solvent universally increases partitioning into octanol
• Co-solvent converts drug into a different chemical species increasing P
• Co-solvent has no effect on partition behavior

Correct Answer: Co-solvent increases aqueous drug solubility, decreasing the apparent partition coefficient

Q14. The Critical Packing Parameter (CPP) is used to predict micellar and aggregate morphology. A CPP value less than ~1/3 predicts which structure?

• Bilayers or vesicles
• Cylindrical micelles
• Spherical micelles
• Inverted hexagonal phase

Correct Answer: Spherical micelles

Q15. Regarding toxicity and regulatory considerations, which statement is generally correct for surfactant selection in pharmaceutical formulations?

• Cationic surfactants are typically less cytotoxic than nonionic surfactants
• Cationic surfactants are often more irritating and more tightly regulated than nonionic surfactants
• All surfactants have identical safety profiles regardless of charge
• Surfactant toxicity is irrelevant for topical formulations

Correct Answer: Cationic surfactants are often more irritating and more tightly regulated than nonionic surfactants

Q16. Which HLB value range is generally recommended to favor formation of oil-in-water (o/w) emulsions?

• Low HLB values (0–6)
• Moderate HLB values (6–8)
• High HLB values (≥10)
• HLB does not influence emulsion type

Correct Answer: High HLB values (≥10)

Q17. During technology transfer of a formulation that uses volatile cosolvents, which issue is most critical to control to maintain drug solubility and batch-to-batch consistency?

• Rate of co-solvent evaporation and final cosolvent concentration in the bulk product
• Color of the product container only
• Manufacturers of surfactant raw materials exclusively
• Magnetic field strength in the production room

Correct Answer: Rate of co-solvent evaporation and final cosolvent concentration in the bulk product

Q18. Which analytical method is particularly suitable for determining CMC of ionic surfactants due to a sharp change in conductivity at micellization?

• Conductivity measurements
• NMR imaging
• Gas chromatography
• Flame photometry for organic surfactants

Correct Answer: Conductivity measurements

Q19. Micellar solubilization capacity for a given surfactant is most closely related to which of the following surfactant characteristics?

• Aggregation number and micelle core volume
• Color index of the surfactant
• Purely the molecular weight of the surfactant headgroup
• Surfactant expiration date

Correct Answer: Aggregation number and micelle core volume

Q20. For quantitative measurement of nonvolatile surfactant concentration in a formulation during scale-up, which analytical approach is commonly applicable in a technology transfer setting?

• HPLC with an appropriate detector (e.g., ELSD or MS) or validated colorimetric/tensiometric methods
• Simple visual inspection of solution clarity only
• Counting micelles under a light microscope
• Measuring room temperature without instrumentation

Correct Answer: HPLC with an appropriate detector (e.g., ELSD or MS) or validated colorimetric/tensiometric methods

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