Dielectric constant and drug stability MCQs With Answer

Dielectric constant and drug stability MCQs With Answer

Understanding the dielectric constant is crucial for B. Pharm students because it links solvent polarity to drug behavior, ionization, solubility, and chemical degradation pathways. The dielectric constant (relative permittivity) influences intermolecular forces, rates of hydrolysis, salt formation, and partitioning in formulations. Knowledge of dielectric effects helps predict how excipients, solvents, and storage conditions affect drug stability, bioavailability, and compatibility. Practical tools such as dielectric spectroscopy and polarity scales inform formulation design and stability testing. This set of focused, application-oriented MCQs covers fundamentals, measurement, and formulation implications so you can apply concepts to real-world pharmaceutics. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What does the dielectric constant (relative permittivity) of a medium measure?

• Its ability to dissolve ionic solids
• Its ability to reduce the effective electric field between charges
• Its conductivity under an alternating current
• Its refractive index for light

Correct Answer: Its ability to reduce the effective electric field between charges

Q2. Which statement best describes the relationship between dielectric constant and solvation of ions?

• Higher dielectric constant solvents stabilize ions by reducing electrostatic attraction
• Lower dielectric constant solvents always increase solubility of salts
• Dielectric constant has no effect on ionic solvation
• Ionic solvation depends only on temperature, not dielectric constant

Correct Answer: Higher dielectric constant solvents stabilize ions by reducing electrostatic attraction

Q3. What is the approximate dielectric constant of water at 25°C often used in pharmaceutics?

• ~2
• ~24
• ~78
• ~150

Correct Answer: ~78

Q4. How does increasing solvent dielectric constant generally affect the ionization of weak acids?

• It shifts equilibrium toward the non-ionized form
• It increases ionization by stabilizing charged species
• It converts acids to bases
• It has no effect on ionization equilibria

Correct Answer: It increases ionization by stabilizing charged species

Q5. Which term correctly describes the dielectric constant unit?

• Coulombs per meter (C/m)
• Farads per meter (F/m)
• Dimensionless (relative value)
• Ohm·meter (Ω·m)

Correct Answer: Dimensionless (relative value)

Q6. In formulation design, why is solvent polarity important for drug stability?

• Polarity affects only the color of the solution
• Polarity alters chemical reaction rates and solvation of reactive species
• Polarity determines molecular weight of the drug
• Polarity is irrelevant if pH is controlled

Correct Answer: Polarity alters chemical reaction rates and solvation of reactive species

Q7. Which solvent would be expected to better stabilize ionic degradation products?

• Benzene (low dielectric)
• Hexane (very low dielectric)
• Water (high dielectric)
• Carbon tetrachloride (low dielectric)

Correct Answer: Water (high dielectric)

Q8. Dielectric spectroscopy in stability studies primarily measures what property?

• Partition coefficient (log P)
• Frequency-dependent permittivity and relaxation processes
• Melting point of the drug
• Viscosity of the formulation

Correct Answer: Frequency-dependent permittivity and relaxation processes

Q9. How does dielectric constant typically change with increasing temperature for polar solvents?

• It increases sharply with temperature
• It stays constant regardless of temperature
• It generally decreases slightly as temperature rises
• It oscillates unpredictably

Correct Answer: It generally decreases slightly as temperature rises

Q10. Which effect explains faster hydrolysis of ionic drugs in high dielectric media?

• Increased hydrophobic interactions
• Enhanced stabilization of charged transition states and intermediates
• Decreased molecular mobility
• Suppression of nucleophiles

Correct Answer: Enhanced stabilization of charged transition states and intermediates

Q11. What is the difference between dielectric constant and dielectric strength?

• They are identical terms used interchangeably
• Dielectric constant is permittivity; dielectric strength is breakdown voltage capacity
• Dielectric constant measures conductivity; dielectric strength measures pH
• Dielectric constant measures color; dielectric strength measures odor

Correct Answer: Dielectric constant is permittivity; dielectric strength is breakdown voltage capacity

Q12. Which formulation problem can arise when using a low dielectric solvent for a salt form drug?

• Improved dissolution of the salt
• Precipitation of the ionic drug as the free base or acid
• Enhanced hydrolytic stability
• Increased ionization of the salt

Correct Answer: Precipitation of the ionic drug as the free base or acid

Q13. How can excipients alter the effective dielectric environment of a formulation?

• By changing ambient pressure only
• By modifying local polarity through hydrogen bonding and dispersion interactions
• Excipients never affect dielectric properties
• Only APIs determine dielectric properties

Correct Answer: By modifying local polarity through hydrogen bonding and dispersion interactions

Q14. Which of the following solvents has a relatively low dielectric constant?

• Dimethyl sulfoxide (DMSO)
• Acetonitrile
• Ethanol
• Benzene

Correct Answer: Benzene

Q15. What impact does a high dielectric medium have on reaction activation energy for ionic reactions?

• It increases activation energy by destabilizing transition states
• It decreases activation energy by stabilizing charged transition states
• It converts ionic reactions to radical reactions
• It has no effect on activation energy

Correct Answer: It decreases activation energy by stabilizing charged transition states

Q16. Which measurement is commonly used to express solvent polarity relevant to drug solubility?

• pKa
• Dielectric constant (relative permittivity)
• Boiling point only
• Optical rotation

Correct Answer: Dielectric constant (relative permittivity)

Q17. In a biphasic extraction, how does dielectric constant influence drug partitioning?

• Higher dielectric organic phase always extracts bases better
• Drugs distribute according to polarity: polar drugs prefer higher dielectric phases
• Dielectric constant is irrelevant to partitioning
• Only density differences govern partitioning

Correct Answer: Drugs distribute according to polarity: polar drugs prefer higher dielectric phases

Q18. Why is water’s high dielectric constant important for biological stability of many drugs?

• It prevents all chemical reactions in solution
• It stabilizes charged biomolecules and facilitates ionic interactions
• It makes water a poor solvent for polar drugs
• It increases flammability of formulations

Correct Answer: It stabilizes charged biomolecules and facilitates ionic interactions

Q19. How can measuring dielectric constant help predict incompatibility between drug and excipient?

• It reveals pH changes directly
• It indicates differences in local polarity that may promote chemical reactions or phase separation
• It measures microbial contamination
• It predicts color changes exactly

Correct Answer: It indicates differences in local polarity that may promote chemical reactions or phase separation

Q20. For a weakly basic drug, which solvent environment will favor the protonated (ionized) form?

• Non-polar, low dielectric solvent
• High dielectric, polar solvent
• Anhydrous apolar oil
• Solid crystalline matrix only

Correct Answer: High dielectric, polar solvent

Q21. Which analytical technique directly probes dielectric relaxation and molecular mobility in formulations?

• Infrared spectroscopy
• Dielectric spectroscopy
• Mass spectrometry
• X-ray diffraction

Correct Answer: Dielectric spectroscopy

Q22. How does incorporation of water into a solid dosage form typically affect local dielectric properties?

• It decreases dielectric constant and reduces mobility
• It increases local dielectric constant and may enhance hydrolytic degradation
• It converts the solid into a gas
• It has no effect on dielectric properties

Correct Answer: It increases local dielectric constant and may enhance hydrolytic degradation

Q23. Which of the following best explains why salts are often more soluble in water than in organic solvents?

• Water has a high dielectric constant that stabilizes separated ions
• Organic solvents react chemically with salts
• Water lowers the temperature of dissolution
• Salts are always non-polar

Correct Answer: Water has a high dielectric constant that stabilizes separated ions

Q24. In accelerated stability testing, considering dielectric effects helps predict what?

• Only photostability but not hydrolysis
• Potential rates of ionization-dependent degradation pathways
• Melting point changes exactly
• Packaging mechanical strength

Correct Answer: Potential rates of ionization-dependent degradation pathways

Q25. Which solvent property often correlates with dielectric constant and affects solubility?

• Polarity and ability to hydrogen-bond
• Optical clarity only
• Magnetic susceptibility
• Color intensity

Correct Answer: Polarity and ability to hydrogen-bond

Q26. For a neutral, lipophilic drug, what dielectric environment typically favors membrane permeation?

• High dielectric hydrophilic environment only
• Low dielectric, lipophilic environment like membrane interior
• Extremely polar solvent like pure water is best
• Dielectric environment does not affect permeation

Correct Answer: Low dielectric, lipophilic environment like membrane interior

Q27. Which experimental factor can change the measured dielectric constant of a formulation?

• Temperature, frequency of measurement, and water content
• Only the color of the container
• Magnetic stirring speed only
• Dielectric constant is immutable once formulation is prepared

Correct Answer: Temperature, frequency of measurement, and water content

Q28. How can high dielectric solvents influence the rate of nucleophilic substitution reactions relevant to degradation?

• They always prevent substitution reactions
• They can stabilize ionic intermediates and increase rates for polar mechanisms
• They convert nucleophiles into electrophiles
• They reduce the solvent’s boiling point only

Correct Answer: They can stabilize ionic intermediates and increase rates for polar mechanisms

Q29. When selecting co-solvents for a parenteral formulation, why is dielectric constant a key consideration?

• It influences ionic strength but not solubility
• It affects solubility, ionization state, and potential chemical stability
• Co-solvents only change osmolarity, not dielectric properties
• Dielectric constant is irrelevant for parenteral use

Correct Answer: It affects solubility, ionization state, and potential chemical stability

Q30. Which strategy can formulators use to reduce hydrolysis of an ionizable drug in aqueous formulations?

• Increase water content to boost dielectric constant
• Choose buffer and co-solvents to lower effective polarity or sequester water
• Always store at higher temperatures
• Convert the drug into a salt that increases ionization in water

Correct Answer: Choose buffer and co-solvents to lower effective polarity or sequester water