Solubilisation MCQs With Answer

Solubilisation MCQs With Answer is a focused resource for B. Pharm students studying drug solubility and formulation strategies. This introduction covers solubility enhancement techniques such as cosolvency, micellar solubilization, complexation with cyclodextrins, pH adjustment, solid dispersions and particle size reduction. It emphasizes key concepts like intrinsic vs apparent solubility, CMC, HLB values, phase-solubility diagrams and dissolution rate factors. Ideal for exam preparation and quick revision, these solubilisation MCQs with answer help build conceptual depth, calculation skills and formulation insight essential for pharmaceutical development. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the best definition of solubilisation in pharmaceutics?

• The process of converting a solid drug into its gaseous form
• The chemical degradation of a drug in solution
• Increase in apparent solubility of a poorly water‑soluble drug using formulation techniques
• The partitioning of drug into lipid membranes

Correct Answer: Increase in apparent solubility of a poorly water‑soluble drug using formulation techniques

Q2. How does intrinsic solubility differ from apparent solubility?

• Intrinsic solubility is measured in organic solvents; apparent is in water
• Intrinsic is solubility of the unionized crystalline form; apparent is total solubility including salts or complexes
• Intrinsic is always higher than apparent solubility
• They are synonymous terms

Correct Answer: Intrinsic is solubility of the unionized crystalline form; apparent is total solubility including salts or complexes

Q3. Which equation is commonly used to relate ionization and aqueous solubility of weak acids and bases?

• Henderson‑Hasselbalch equation
• Nernst equation
• Van’t Hoff equation
• Arrhenius equation

Correct Answer: Henderson‑Hasselbalch equation

Q4. What happens to the solubility of a weak acid when pH increases above its pKa?

• Solubility decreases because more drug is unionized
• Solubility increases because more drug is ionized
• Solubility is independent of pH
• Solubility becomes zero

Correct Answer: Solubility increases because more drug is ionized

Q5. Which technique involves adding water‑miscible organic solvents (e.g., ethanol) to increase drug solubility?

• Micellar solubilization
• Complexation with cyclodextrins
• Cosolvency
• Solid dispersion

Correct Answer: Cosolvency

Q6. Which property of the solvent primarily changes during cosolvency to enhance solubility?

• pH
• Dielectric constant
• Viscosity only
• Surface tension only

Correct Answer: Dielectric constant

Q7. What is the critical micelle concentration (CMC)?

• The concentration of surfactant at which solubility is minimal
• The concentration of surfactant above which micelles form and solubilization increases
• The total concentration of drug that can be solubilized
• The pH at which surfactants ionize

Correct Answer: The concentration of surfactant above which micelles form and solubilization increases

Q8. Which region of a micelle typically solubilizes hydrophobic drugs?

• Hydrophilic corona
• Hydrophobic core
• Outer Stern layer
• Counter‑ion shell

Correct Answer: Hydrophobic core

Q9. Hydrotropy refers to which solubilisation mechanism?

• Formation of covalent complexes between drug and solvent
• Use of high concentrations of certain small amphiphilic molecules to increase aqueous solubility
• Prodrug formation to enhance lipophilicity
• Particle size reduction by milling

Correct Answer: Use of high concentrations of certain small amphiphilic molecules to increase aqueous solubility

Q10. Cyclodextrins improve solubility primarily by which mechanism?

• Covalent bonding to drug molecules
• Inclusion complexation with the drug accommodated in the cyclodextrin cavity
• Raising the solution pH
• Forming micelles

Correct Answer: Inclusion complexation with the drug accommodated in the cyclodextrin cavity

Q11. What does a phase‑solubility diagram type A indicate in Higuchi‑Connors classification?

• Drug precipitates out at any added cyclodextrin
• Linear increase of solubility with cyclodextrin concentration, indicating soluble complex formation
• No change in solubility with cyclodextrin
• Exponential decrease in solubility

Correct Answer: Linear increase of solubility with cyclodextrin concentration, indicating soluble complex formation

Q12. Which slope value in a phase‑solubility plot generally suggests a 1:1 drug:cyclodextrin complex?

• A slope greater than 1
• A slope between 0 and 1 with linear A_L type behaviour
• A negative slope
• No slope, flat line

Correct Answer: A slope between 0 and 1 with linear A_L type behaviour

Q13. Solid dispersions enhance solubility primarily by which factor?

• Increasing crystallinity of the drug
• Converting the drug to an amorphous high‑energy form and improving wettability
• Lowering the pH of the environment
• Forming large crystals

Correct Answer: Converting the drug to an amorphous high‑energy form and improving wettability

Q14. Which of the following is a common method to reduce particle size and increase solubility/dissolution rate?

• Spray drying only for gases
• Micronization or nanonization
• Freeze drying of the solvent only
• Lyophilization of pure crystals without matrix

Correct Answer: Micronization or nanonization

Q15. The Noyes‑Whitney equation describes which aspect related to solubility?

• Rate of chemical degradation in solution
• Dissolution rate of solids into a solvent
• pKa determination from solubility data
• Micelle formation kinetics

Correct Answer: Dissolution rate of solids into a solvent

Q16. Salting‑out effect causes what change in solubility of a non‑electrolyte drug when salt concentration increases?

• Solubility increases due to better hydration
• Solubility decreases because water activity is reduced
• Solubility becomes infinite
• No effect of salts on solubility

Correct Answer: Solubility decreases because water activity is reduced

Q17. Which parameter indicates the balance between hydrophilic and lipophilic portions of a surfactant?

• Critical micelle concentration (CMC)
• Hydrophilic‑lipophilic balance (HLB)
• Partition coefficient (log P)
• Dielectric constant

Correct Answer: Hydrophilic‑lipophilic balance (HLB)

Q18. Yalkowsky’s log‑linear cosolvency model relates drug solubility to what variable?

• Temperature only
• Volume fraction of cosolvent
• pH only
• Surfactant molecular weight

Correct Answer: Volume fraction of cosolvent

Q19. Which of the following is a typical water‑miscible cosolvent used to improve solubility?

• Hexane
• Ethanol
• Squalene
• Sodium chloride

Correct Answer: Ethanol

Q20. Mixed micelles are advantageous because they:

• Always decrease solubilisation capacity
• Can reduce CMC and increase solubilisation for certain drugs
• Prevent any drug from dissolving
• Are not used in pharmaceutical formulations

Correct Answer: Can reduce CMC and increase solubilisation for certain drugs

Q21. Which analytical technique is most suitable to detect crystalline-to-amorphous conversion in solid dispersions?

• UV‑Visible spectroscopy
• Differential scanning calorimetry (DSC) and X‑ray diffraction (XRD)
• pH titration
• Partition coefficient measurement

Correct Answer: Differential scanning calorimetry (DSC) and X‑ray diffraction (XRD)

Q22. In cyclodextrin complexation, an apparent 1:1 stability constant (K1:1) of higher value implies what?

• Weaker complexation between drug and cyclodextrin
• Stronger affinity and more stable complex formation
• No complex formation
• Lower solubility of the drug

Correct Answer: Stronger affinity and more stable complex formation

Q23. Which strategy can be used to enhance solubility of a basic drug?

• Raise pH to above pKa
• Lower pH to form salts
• Convert to non‑ionizable prodrug only
• Remove all solvent

Correct Answer: Lower pH to form salts

Q24. The term “apparent solubility” of a weak electrolyte refers to:

• Solubility of the pure unionized form only
• Total concentration of drug in solution including ionized and unionized species
• Solubility measured in non‑aqueous solvents only
• Solubility at infinite dilution only

Correct Answer: Total concentration of drug in solution including ionized and unionized species

Q25. Which of these will most likely increase dissolution rate according to Noyes‑Whitney?

• Decreasing surface area of the drug particles
• Decreasing diffusion coefficient
• Increasing agitation or stirring to reduce boundary layer thickness
• Lowering solubility of the drug

Correct Answer: Increasing agitation or stirring to reduce boundary layer thickness

Q26. Which phenomenon describes increased solubility of hydrophobic drugs in presence of certain salts due to specific ion‑drug interactions?

• Salting‑out
• Salting‑in
• Hydrophobic collapse
• Coacervation

Correct Answer: Salting‑in

Q27. What is the expected effect of converting a crystalline drug to its amorphous form on solubility?

• Amorphous form usually has higher apparent solubility than crystalline form
• No change in solubility
• Amorphous form always has lower solubility
• Crystalline form dissolves faster

Correct Answer: Amorphous form usually has higher apparent solubility than crystalline form

Q28. Which of the following is NOT a typical solubilisation excipient?

• Sodium lauryl sulfate (surfactant)
• Hydroxypropyl‑β‑cyclodextrin (complexing agent)
• Glycerol (cosolvent component)
• Sodium chloride as a direct surfactant

Correct Answer: Sodium chloride as a direct surfactant

Q29. The slope of a log solubility vs cosolvent fraction plot in Yalkowsky model is typically:

• Zero for all drugs
• Positive indicating increased solubility with cosolvent
• Negative indicating decreased solubility with cosolvent
• Infinite

Correct Answer: Positive indicating increased solubility with cosolvent

Q30. Which approach uses lipid vehicles to improve oral absorption of poorly soluble drugs?

• Lipid‑based formulations such as SMEDDS or emulsions
• Using only high pH aqueous buffers
• Solid crystalline excipient embedding
• Direct compression into tablets without excipients

Correct Answer: Lipid‑based formulations such as SMEDDS or emulsions

Q31. What is the primary role of surfactants in oral solubilisation?

• To reduce drug chemical stability
• To form micelles that can solubilize lipophilic drugs and improve wetting
• To crystallize the drug more effectively
• To decompose the active ingredient

Correct Answer: To form micelles that can solubilize lipophilic drugs and improve wetting

Q32. Which factor does NOT directly affect micellar solubilization capacity?

• Surfactant concentration relative to CMC
• Nature of the drug (hydrophobicity)
• Temperature
• Color of the formulation container

Correct Answer: Color of the formulation container

Q33. In calculating fold solubility enhancement, you divide solubility in formulation by:

• Solubility of placebo
• Intrinsic solubility in pure water or control solubility
• Volume of dissolution medium
• Molecular weight of the drug

Correct Answer: Intrinsic solubility in pure water or control solubility

Q34. Which of the following drugs is a classical example of a poorly water‑soluble compound often discussed in solubilisation studies?

• Acetaminophen (paracetamol)
• Phenytoin
• Sodium chloride
• Metformin

Correct Answer: Phenytoin

Q35. Which experimental method directly measures saturation solubility?

• Shake‑flask method with excess solid until equilibrium
• Single point UV of a dilute solution only
• Measuring viscosity of a solution
• Calculating from log P only

Correct Answer: Shake‑flask method with excess solid until equilibrium

Q36. According to van’t Hoff equation, increasing temperature generally does what to solubility of most solids?

• Decreases solubility for all solids
• Increases solubility for endothermic dissolution processes
• Makes solubility independent of temperature
• Converts solids to gases

Correct Answer: Increases solubility for endothermic dissolution processes

Q37. What is the main concern when using high concentrations of cosolvents or surfactants in formulations?

• They always make the drug unstable chemically
• Possible toxicity, irritation and regulatory limits for excipient use
• They convert drug to a gas
• They never affect bioavailability

Correct Answer: Possible toxicity, irritation and regulatory limits for excipient use

Q38. Which parameter describes the tendency of a drug to partition between octanol and water and influences solubility strategies?

• pKa only
• Log P or log D
• CMC only
• Dielectric constant of water only

Correct Answer: Log P or log D

Q39. Prodrug approach to enhance solubility works by:

• Directly increasing pKa only
• Covalently modifying the drug to a more hydrophilic form that is metabolized to active drug in vivo
• Removing functional groups permanently
• Making the drug more crystalline

Correct Answer: Covalently modifying the drug to a more hydrophilic form that is metabolized to active drug in vivo

Q40. What does the term “apparent partition coefficient (log D)” reflect?

• Partitioning of an ionizable drug between octanol and water at a specific pH including ionization
• Partitioning ignoring ionization entirely
• Only the solubility in water
• Only the molecular weight of drug

Correct Answer: Partitioning of an ionizable drug between octanol and water at a specific pH including ionization

Q41. Which excipient class is commonly used to form solid dispersions with a drug?

• Cellulose derivatives like HPMC
• Inert gases
• High molecular weight salts only
• Pure metals

Correct Answer: Cellulose derivatives like HPMC

Q42. Which of the following is a sign of precipitation or instability when trying to solubilize a drug in a formulation?

• Clear and stable solution over time
• Formation of crystals or turbidity upon dilution or storage
• Increased bioavailability always
• Lowered density of the solution

Correct Answer: Formation of crystals or turbidity upon dilution or storage

Q43. In micellar solubilisation, the linear partition model relates solubilized drug concentration to:

• Drug pKa only
• Surfactant concentration above CMC through a partition coefficient between micelle and aqueous phase
• Temperature only
• Drug molecular weight only

Correct Answer: Surfactant concentration above CMC through a partition coefficient between micelle and aqueous phase

Q44. How does increasing ionic strength generally affect solubility of ionic drugs?

• Ionic strength has no effect
• Can either increase or decrease solubility depending on ion interactions (salting‑in or salting‑out)
• Always increases solubility for all ionic drugs
• Always decreases solubility for all ionic drugs

Correct Answer: Can either increase or decrease solubility depending on ion interactions (salting‑in or salting‑out)

Q45. Which of these is a common laboratory method to study micelle formation and determine CMC?

• pH titration only
• Surface tension or conductivity measurements
• Measuring tablet hardness
• DSC only

Correct Answer: Surface tension or conductivity measurements

Q46. A phase‑solubility plot shows downward curvature (B‑type). What does this often indicate?

• Formation of insoluble complex or limited solubility of complex
• Infinite linear increase in solubility
• No interaction between drug and complexing agent
• Perfect 1:1 soluble complex formation

Correct Answer: Formation of insoluble complex or limited solubility of complex

Q47. Drug nanocrystals improve solubility/dissolution primarily by:

• Decreasing surface area
• Increasing surface area and saturation solubility via size reduction
• Converting drug into a gas phase
• Eliminating the need for excipients

Correct Answer: Increasing surface area and saturation solubility via size reduction

Q48. Which statement about HLB value selection is true for forming oil‑in‑water emulsions?

• Low HLB surfactants (3–6) are preferred for oil‑in‑water emulsions
• High HLB surfactants (8–18) are preferred for oil‑in‑water emulsions
• HLB has no relevance to emulsion type
• Only ionic strength matters for emulsions

Correct Answer: High HLB surfactants (8–18) are preferred for oil‑in‑water emulsions

Q49. Which calculation estimates the fraction of unionized drug at a given pH for a weak acid?

• Use Arrhenius equation
• Use Henderson‑Hasselbalch to calculate fraction unionized = 1 / (1 + 10^(pH‑pKa))
• Use van’t Hoff equation directly
• Use partition coefficient formula only

Correct Answer: Use Henderson‑Hasselbalch to calculate fraction unionized = 1 / (1 + 10^(pH‑pKa))

Q50. From a regulatory and safety perspective, what must formulators consider when selecting solubilising agents?

• Only cost of the excipient
• Toxicity, permissible daily exposure, route of administration and compatibility with drug
• Only the excipient’s color
• That excipients never interact with the drug

Correct Answer: Toxicity, permissible daily exposure, route of administration and compatibility with drug

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