Physical properties of drugs MCQs With Answer

Understanding the physical properties of drugs is essential for B.Pharm students involved in drug formulation, stability assessment, and drug delivery design. This concise overview highlights key concepts including solubility, dissolution rate, partition coefficient (log P/log D), pKa and pH-dependent ionization, polymorphism, melting point, hygroscopicity, particle size, surface tension, and solid-state behavior. Mastery of these properties guides selection of salts, solvents, and excipients, impacts bioavailability, and informs stability and manufacturing processes. Familiarity with micromeritics, wettability, and BCS classification further supports rational formulation development. These core topics directly influence pharmacokinetics and product performance. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which statement best defines aqueous solubility of a drug?

• The maximum mass of drug that can be dissolved in a given volume of solvent at equilibrium
• The rate at which a drug dissolves in the gastrointestinal tract
• The partitioning of a drug between octanol and water
• The pH at which a drug is 50% ionized

Correct Answer: The maximum mass of drug that can be dissolved in a given volume of solvent at equilibrium

Q2. According to the Noyes‑Whitney equation, which factor directly increases the dissolution rate of a poorly soluble drug?

• Increase in particle surface area
• Decrease in intrinsic solubility
• Decrease in diffusion coefficient
• Decrease in agitation

Correct Answer: Increase in particle surface area

Q3. The octanol–water partition coefficient (log P) primarily measures which property of a neutral drug?

• Lipophilicity
• Acid dissociation constant
• Solid-state crystallinity
• Hygroscopic tendency

Correct Answer: Lipophilicity

Q4. Which equation relates pH, pKa and the ratio of ionized to unionized species for a weak acid?

• Henderson–Hasselbalch equation
• Noyes–Whitney equation
• Partition coefficient equation
• Arrhenius equation

Correct Answer: Henderson–Hasselbalch equation

Q5. How does an amorphous form of a drug commonly compare to its crystalline polymorph?

• Amorphous form usually has higher apparent solubility and lower physical stability
• Amorphous form has lower solubility and higher melting point
• Amorphous form is always more chemically stable
• Amorphous form exhibits a sharp melting point

Correct Answer: Amorphous form usually has higher apparent solubility and lower physical stability

Q6. Which physical property is often used as an indicator of purity and crystal lattice strength?

• Melting point
• Optical rotation
• Surface tension
• Vapor pressure

Correct Answer: Melting point

Q7. Which term describes a solid drug that absorbs moisture from the air until it dissolves to form a solution?

• Deliquescence
• Efflorescence
• Hygroscopicity
• Desiccation

Correct Answer: Deliquescence

Q8. Reducing particle size of a drug powder most directly affects which of the following?

• Increase in dissolution rate due to larger surface area
• Decrease in chemical stability due to lower pKa
• Decrease in partition coefficient (log P)
• Increase in melting point

Correct Answer: Increase in dissolution rate due to larger surface area

Q9. Carr’s index and Hausner ratio are used to assess which powder property?

• Flowability and compressibility
• Solubility in water
• Hygroscopicity
• Surface tension

Correct Answer: Flowability and compressibility

Q10. Wettability of a solid by a liquid is best characterized by which measurement?

• Contact angle between liquid and solid surface
• Partition coefficient of drug
• Melting point depression
• Optical rotation

Correct Answer: Contact angle between liquid and solid surface

Q11. How does log D differ from log P for ionizable drugs?

• Log D is pH‑dependent and accounts for ionized and unionized species
• Log D is measured only for nonionizable drugs
• Log D equals log P plus pKa
• Log D measures solid state crystallinity

Correct Answer: Log D is pH‑dependent and accounts for ionized and unionized species

Q12. Biopharmaceutics Classification System (BCS) classifies drugs based on which two properties?

• Solubility and intestinal permeability
• Partition coefficient and melting point
• pKa and intrinsic dissolution rate
• Particle size and hygroscopicity

Correct Answer: Solubility and intestinal permeability

Q13. What is Ostwald ripening in solid dispersions or suspensions?

• Growth of larger particles at the expense of smaller ones due to solubility differences
• Spontaneous evaporation of solvent from crystals
• Conversion of an amorphous drug to salt form
• Immediate dissolution of crystalline particles

Correct Answer: Growth of larger particles at the expense of smaller ones due to solubility differences

Q14. The glass transition temperature (Tg) is most relevant to which state of a drug?

• Amorphous solids
• Perfect single crystals
• Gas phase volatilized drug
• Highly ordered polymorphs only

Correct Answer: Amorphous solids

Q15. Salt formation of a weakly acidic drug typically improves which property?

• Aqueous solubility of the drug
• Chemical stability against hydrolysis
• Partition coefficient in octanol
• Optical activity

Correct Answer: Aqueous solubility of the drug

Q16. Which form (ionized or unionized) of a drug generally permeates biological membranes more readily by passive diffusion?

• Unionized form
• Ionized form
• Both permeate equally
• Only zwitterionic form permeates

Correct Answer: Unionized form

Q17. According to general solubility behavior, increasing temperature usually has what effect on solubility of solids in liquids?

• Solubility generally increases with temperature for most solids
• Solubility always decreases with temperature
• Solubility is independent of temperature
• Solubility becomes zero at higher temperatures

Correct Answer: Solubility generally increases with temperature for most solids

Q18. High vapor pressure of a drug substance indicates which concern during formulation?

• Volatility leading to loss during processing and storage
• Increased aqueous solubility
• Enhanced tablet compressibility
• Greater crystal lattice energy

Correct Answer: Volatility leading to loss during processing and storage

Q19. Enantiomers of a chiral drug can differ in which physical or biological properties?

• Optical rotation, receptor binding, and sometimes solubility
• Melting point always identical and bioactivity identical
• Partition coefficient is always equal for enantiomers
• Hygroscopicity is always higher for the R‑enantiomer

Correct Answer: Optical rotation, receptor binding, and sometimes solubility

Q20. A high Hausner ratio indicates which characteristic of a powder?

• Poor flowability and high cohesiveness
• Excellent flow and low compressibility
• High solubility in water
• Low melting point

Correct Answer: Poor flowability and high cohesiveness

Q21. The Hildebrand solubility parameter helps in selecting excipients by predicting what?

• Solvent–solute miscibility based on cohesive energy density
• The drug’s pKa in aqueous media
• The diffusion coefficient in blood
• The drug’s crystalline habit

Correct Answer: Solvent–solute miscibility based on cohesive energy density

Q22. Specific surface area (SSA) of a powder is most important because it influences which property?

• Dissolution rate and chemical reactivity
• Optical rotation
• pKa value
• BCS classification directly

Correct Answer: Dissolution rate and chemical reactivity

Q23. Which excipient type is commonly used to improve wetting and reduce surface tension of aqueous media for poorly wettable drugs?

• Surfactants (wetting agents)
• Bulking agents
• Binders
• Desiccants

Correct Answer: Surfactants (wetting agents)

Q24. An amphoteric drug shows which solubility behavior over pH range?

• Minimum solubility near its isoelectric point with increased solubility at low and high pH
• Constant solubility across all pH values
• Maximum solubility only at neutral pH
• Solubility independent of pKa values

Correct Answer: Minimum solubility near its isoelectric point with increased solubility at low and high pH

Q25. A metastable polymorph compared to the stable polymorph typically exhibits which combination?

• Higher solubility and lower thermodynamic stability
• Lower solubility and higher stability
• Identical solubility and stability
• Lower melting point but greater stability

Correct Answer: Higher solubility and lower thermodynamic stability

Q26. Which condition is essential to maintain sink conditions during an in vitro dissolution test?

• Volume of dissolution medium much greater than the drug solubility amount
• Stirring speed set to zero
• Drug concentration equal to its saturation solubility
• Use of non‑aqueous medium only

Correct Answer: Volume of dissolution medium much greater than the drug solubility amount

Q27. For central nervous system penetration, which physical properties of a drug are most favorable?

• Moderate lipophilicity and low ionization at physiological pH
• Very high molecular weight and high polarity
• High hygroscopicity and high melting point
• High degree of crystallinity and no lipophilicity

Correct Answer: Moderate lipophilicity and low ionization at physiological pH

Q28. Which behavior best describes efflorescent drug substances?

• They lose water of crystallization to the atmosphere forming a powdery surface
• They absorb moisture and dissolve to form a liquid
• They sublimate at room temperature
• They become more lipophilic on exposure to air

Correct Answer: They lose water of crystallization to the atmosphere forming a powdery surface

Q29. A low melting point drug is more likely to exhibit which stability issue during processing?

• Thermal degradation or melting during high‑temperature operations
• Greater resistance to hydrolysis
• Lower propensity for polymorphic transformation
• Higher optical rotation values

Correct Answer: Thermal degradation or melting during high‑temperature operations

Q30. How does crystal habit affect powder processing in tablet manufacture?

• Needle‑shaped crystals often cause poor flow and compaction issues
• Equant crystals always improve solubility
• Plate‑like crystals ensure optimal wettability without additives
• Crystal habit has no effect on blend uniformity

Correct Answer: Needle‑shaped crystals often cause poor flow and compaction issues

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