Electrical properties of colloids MCQs With Answer

The electrical properties of colloids are central to understanding colloidal stability, formulation design, and drug delivery in pharmaceutical science. This introduction explains key concepts such as zeta potential, electrophoresis, electrokinetic phenomena, Debye length, and the influence of pH, ionic strength and surfactants on colloidal stability. B.Pharm students will learn how surface charge, DLVO theory, and measurement techniques (microelectrophoresis, zeta sizer, conductometry) determine aggregation, flocculation and performance of suspensions, emulsions, and nanoparticles in formulations. Practical implications for formulation optimization, stability testing and regulatory considerations are emphasized. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is zeta potential in colloidal systems?

• The electric potential at the surface of the particle
• The potential difference between bulk solution and slip plane
• The total charge on the colloidal particle
• The ionic strength of the dispersion medium

Correct Answer: The potential difference between bulk solution and slip plane

Q2. Which technique is commonly used to measure electrophoretic mobility of colloidal particles?

• UV-Vis spectrophotometry
• Dynamic light scattering
• Microelectrophoresis / Laser Doppler electrophoresis
• Atomic absorption spectroscopy

Correct Answer: Microelectrophoresis / Laser Doppler electrophoresis

Q3. According to DLVO theory, which two forces primarily determine colloidal stability?

• Hydrophobic and steric forces
• Van der Waals attraction and electrostatic repulsion
• Viscous drag and buoyancy
• Magnetic attraction and gravitational forces

Correct Answer: Van der Waals attraction and electrostatic repulsion

Q4. The Smoluchowski equation is applied to calculate zeta potential from electrophoretic mobility when particles are:

• Much smaller than the Debye length (thin double layer)
• Comparable to the mean free path of solvent molecules
• Large compared to Debye length (thick double layer)
• In a nonpolar solvent only

Correct Answer: Large compared to Debye length (thick double layer)

Q5. Increasing ionic strength of the medium generally leads to:

• Increase in Debye length
• Compression of the electrical double layer
• Higher zeta potential magnitude
• Decreased van der Waals attraction

Correct Answer: Compression of the electrical double layer

Q6. Which factor most directly shifts the isoelectric point (IEP) of colloidal particles?

• Temperature change only
• Adsorption of specific ions or surfactants
• Change in container shape
• Presence of light

Correct Answer: Adsorption of specific ions or surfactants

Q7. Electrophoretic mobility is defined as:

• The velocity of particle divided by applied electric field
• The charge density of the particle surface
• The conductivity of the dispersion medium
• The refractive index change under electric field

Correct Answer: The velocity of particle divided by applied electric field

Q8. Which statement about Debye length is correct?

• It increases with increasing ionic strength
• It represents the thickness of the diffuse double layer
• It is independent of temperature
• It is the distance between particle centers at coagulation

Correct Answer: It represents the thickness of the diffuse double layer

Q9. In pharmaceutical suspensions, high absolute zeta potential (e.g., > |30| mV) generally implies:

• Faster sedimentation
• Better electrostatic stabilization against aggregation
• Complete flocculation
• High viscosity regardless of formulation

Correct Answer: Better electrostatic stabilization against aggregation

Q10. The Hückel approximation for electrophoresis applies when:

• Particle radius is much larger than Debye length (κa >> 1)
• Particle radius is much smaller than Debye length (κa << 1)
• Particles are conducting spheres only
• Only for nonionic particles

Correct Answer: Particle radius is much smaller than Debye length (κa << 1)

Q11. Which electrokinetic phenomenon is responsible for liquid flow induced by an applied electric field across a charged capillary?

• Electrophoresis
• Electro-osmosis
• Streaming potential
• Thermophoresis

Correct Answer: Electro-osmosis

Q12. Streaming potential arises when:

• A shear flow induces movement of counterions relative to a stationary charged surface
• Particles migrate under thermal gradients
• An electric field causes particle rotation
• Light causes charge separation

Correct Answer: A shear flow induces movement of counterions relative to a stationary charged surface

Q13. Steric stabilization of colloids is achieved by:

• Adsorption of nonionic polymers creating a protective layer
• Increasing salt concentration to high levels
• Reducing particle surface area
• Increasing gravitational forces

Correct Answer: Adsorption of nonionic polymers creating a protective layer

Q14. Which of the following increases electrophoretic mobility for a given zeta potential?

• Higher viscosity of medium
• Lower viscosity of medium
• Higher particle size only
• Presence of multivalent counterions

Correct Answer: Lower viscosity of medium

Q15. The point of zero charge (PZC) differs from isoelectric point (IEP) because:

• PZC is measured only in nonpolar solvents
• PZC refers to surface charge neutrality while IEP refers to zero electrophoretic mobility
• They are identical terms with no difference
• IEP applies only to proteins

Correct Answer: PZC refers to surface charge neutrality while IEP refers to zero electrophoretic mobility

Q16. In DLVO energy profile, a primary minimum corresponds to:

• Weak reversible attraction leading to flocculation
• Strong irreversible aggregation at close approach
• Maximum energy barrier preventing aggregation
• Region of purely repulsive forces

Correct Answer: Strong irreversible aggregation at close approach

Q17. Which ion valence has the greatest effect on compressing the double layer and promoting coagulation?

• Monovalent (1+)
• Divalent (2+)
• Trivalent (3+)
• The valence does not matter

Correct Answer: Trivalent (3+)

Q18. For a given colloidal formulation, addition of a nonionic surfactant typically affects electrical properties by:

• Directly increasing zeta potential magnitude due to ionic charge
• Providing steric hindrance and possibly masking surface charge
• Generating free radicals that change conductivity
• Removing the electrical double layer completely

Correct Answer: Providing steric hindrance and possibly masking surface charge

Q19. Which parameter is directly measured by a Zetasizer instrument to estimate zeta potential?

• Particle number concentration
• Electrophoretic mobility
• Thermal conductivity
• Optical absorbance

Correct Answer: Electrophoretic mobility

Q20. What is the effect of increasing temperature on zeta potential and colloidal stability in most aqueous systems?

• Always increases zeta potential magnitude and stabilizes
• Can decrease viscosity and alter mobility; stability effect depends on system
• Has no effect on electrical properties
• Instantly precipitates all colloids

Correct Answer: Can decrease viscosity and alter mobility; stability effect depends on system

Q21. Which equation relates ionic strength to Debye length in a given medium?

• Stokes-Einstein equation
• Debye-Hückel relation
• Arrhenius equation
• Nernst equation

Correct Answer: Debye-Hückel relation

Q22. What term describes charged layer tightly bound to the particle surface?

• Diffuse layer
• Gouy-Chapman layer
• Stern layer (or compact layer)
• Bulk ionic layer

Correct Answer: Stern layer (or compact layer)

Q23. Which of the following will most likely lower the zeta potential magnitude of negatively charged particles?

• Addition of a low concentration of monovalent salt
• Addition of a high concentration of multivalent cations
• Decrease in pH if surface remains negatively charged
• Adding nonionic polymer in trace amounts

Correct Answer: Addition of a high concentration of multivalent cations

Q24. What is the main practical importance of measuring conductivity in colloidal dispersions?

• To determine optical clarity only
• To estimate ionic strength and monitor electrolyte content affecting electrical double layer
• To measure particle size directly
• To quantify polymer molecular weight

Correct Answer: To estimate ionic strength and monitor electrolyte content affecting electrical double layer

Q25. Which phenomenon explains motion of charged particles toward an electrode under applied electric field?

• Thermophoresis
• Electrophoresis
• Osmosis
• Diffusiophoresis

Correct Answer: Electrophoresis

Q26. Which additive provides electrostatic stabilization to anionic colloidal particles?

• Adding small amounts of trivalent cations
• Adsorption of anionic surfactants increasing negative surface charge
• Adding high molecular weight nonionic polymers only
• Reducing pH to extremely low values always

Correct Answer: Adsorption of anionic surfactants increasing negative surface charge

Q27. If zeta potential of a suspension changes from -40 mV to -5 mV after adding salt, the suspension is likely to:

• Become more stable due to screening
• Undergo rapid coagulation or flocculation
• Show no change in physical behavior
• Instantly evaporate

Correct Answer: Undergo rapid coagulation or flocculation

Q28. Which factor does NOT influence electrophoretic mobility?

• Dielectric constant of medium
• Viscosity of medium
• Applied electric field strength (in linear regime mobility is independent of field strength)
• Particle surface charge and zeta potential

Correct Answer: Applied electric field strength (in linear regime mobility is independent of field strength)

Q29. Which pharmaceutical colloid is an example where electrical properties are critical for stability?

• Dry powder tablets exclusively
• O/W emulsions and nanosuspensions
• Pure crystalline APIs in solid state
• Sterile water for injection

Correct Answer: O/W emulsions and nanosuspensions

Q30. The Henry function in electrophoresis bridges which two limiting cases?

• Hydrophobic and hydrophilic surfaces
• Smoluchowski (κa >> 1) and Hückel (κa << 1) limits
• DLVO and non-DLVO forces
• Electrostatic and magnetic forces

Correct Answer: Smoluchowski (κa >> 1) and Hückel (κa << 1) limits

Q31. Which measurement can help distinguish between flocculated and deflocculated suspensions?

• Viscosity only
• Particle size distribution and zeta potential
• Colorimetry
• pH meter reading only

Correct Answer: Particle size distribution and zeta potential

Q32. In charged liposomal formulations, control of surface charge affects:

• Only the color of liposomes
• Stability, biodistribution, and cellular uptake
• Combustibility of formulation
• Viscosity above 1000 cP exclusively

Correct Answer: Stability, biodistribution, and cellular uptake

Q33. Which of the following best describes electrophoretic deposition in pharmaceutics?

• Deposition of charged particles onto an electrode under electric field, used in coatings
• Precipitation by adding a nonsolvent
• Spray drying of colloids
• Thermal sintering of particles

Correct Answer: Deposition of charged particles onto an electrode under electric field, used in coatings

Q34. What role does counterion condensation play in colloidal electrics?

• It increases particle size directly
• It reduces effective surface charge by ion binding, lowering zeta potential
• It always makes particles positively charged
• It eliminates van der Waals forces

Correct Answer: It reduces effective surface charge by ion binding, lowering zeta potential

Q35. Which ionic condition favors maximum electrical double layer thickness?

• High salt concentration with multivalent ions
• Very low ionic strength (dilute electrolyte)
• Presence of organic solvents only
• High pH irrespective of ions

Correct Answer: Very low ionic strength (dilute electrolyte)

Q36. Which is a non-DLVO force important in stabilizing pharmaceutical colloids?

• Magnetic attraction
• Steric hindrance due to adsorbed polymers
• Purely gravitational forces
• Elastic modulus of the container

Correct Answer: Steric hindrance due to adsorbed polymers

Q37. Adsorption of proteins onto nanoparticle surfaces commonly alters electrical properties by:

• Always increasing positive charge
• Changing surface charge and zeta potential depending on protein isoelectric point and orientation
• Removing all surface charges instantly
• Preventing any interaction with biological membranes

Correct Answer: Changing surface charge and zeta potential depending on protein isoelectric point and orientation

Q38. What is electrophoretic light scattering used for in colloid characterization?

• Measuring thermal conductivity
• Determining electrophoretic mobility and zeta potential
• Assessing pH only
• Quantifying API potency

Correct Answer: Determining electrophoretic mobility and zeta potential

Q39. A positive streaming potential indicates:

• Net negative surface charge on channel walls
• Net positive charge on channel walls
• No net charge on surfaces
• That the liquid is nonpolar

Correct Answer: Net positive charge on channel walls

Q40. Which process can reverse the sign of zeta potential of colloidal particles?

• Adsorption of oppositely charged polyelectrolyte beyond neutralization
• Lowering ionic strength only
• Reducing particle concentration only
• Decreasing temperature by 1°C

Correct Answer: Adsorption of oppositely charged polyelectrolyte beyond neutralization

Q41. In a nanoparticle suspension, high polydispersity index (PDI) combined with low absolute zeta potential suggests:

• Excellent long-term stability
• High risk of aggregation and instability
• That particles are all the same size
• Charge neutrality with no practical effects

Correct Answer: High risk of aggregation and instability

Q42. Which solvent property enhances electrophoretic mobility for a given zeta potential?

• Higher dielectric constant and lower viscosity
• Lower dielectric constant and higher viscosity
• Purely nonpolar nature
• Higher refractive index only

Correct Answer: Higher dielectric constant and lower viscosity

Q43. How does pH influence colloidal electrical properties?

• It alters ionization of surface groups, changing surface charge and zeta potential
• It only affects color and has no electrical effect
• It changes particle mass directly
• It only matters for gaseous colloids

Correct Answer: It alters ionization of surface groups, changing surface charge and zeta potential

Q44. Which experimental artifact can lead to incorrect zeta potential readings?

• Using an appropriate electrolyte concentration
• Particle sedimentation or multiple scattering during measurement
• Ensuring sample conductivity is within instrument range
• Calibrating instrument with standards

Correct Answer: Particle sedimentation or multiple scattering during measurement

Q45. The Stern layer contributes to which of the following?

• The outer diffuse electrical potential only
• Compact layer of specifically adsorbed ions, affecting surface charge
• Viscous drag on particles exclusively
• Optical absorbance of colloid

Correct Answer: Compact layer of specifically adsorbed ions, affecting surface charge

Q46. Which surface modification is commonly used to increase circulation time of nanoparticles in vivo by affecting electrical properties?

• Coating with polyethylene glycol (PEG) to provide steric barrier and reduce opsonization
• Adding high concentrations of sodium chloride
• Functionalizing with strong multivalent cationic groups only
• Heating particles to 200°C

Correct Answer: Coating with polyethylene glycol (PEG) to provide steric barrier and reduce opsonization

Q47. Which parameter is most useful to predict aggregation tendency under physiological conditions?

• Zeta potential measured in pure water only
• Zeta potential measured in simulated biological fluids and ionic conditions
• API potency
• Ambient light intensity

Correct Answer: Zeta potential measured in simulated biological fluids and ionic conditions

Q48. During formulation, bridging flocculation is caused by:

• Small surfactant molecules only
• High molecular weight polymers adsorbing onto multiple particles forming bridges
• Strictly electrostatic repulsion
• Low molecular weight salt addition only

Correct Answer: High molecular weight polymers adsorbing onto multiple particles forming bridges

Q49. Which of the following describes zeta potential titration?

• Gradual change of ionic conditions or pH while monitoring zeta potential to find IEP
• Titration of API concentration only
• Measuring color change during titration
• A thermal analysis technique

Correct Answer: Gradual change of ionic conditions or pH while monitoring zeta potential to find IEP

Q50. In designing stable nanoparticle drug carriers, an integrated electrical strategy includes:

• Ignoring surface charge and focusing only on shape
• Optimizing surface charge, steric coating, and measuring zeta potential under relevant conditions
• Using only organic solvents in all cases
• Avoiding any characterization studies

Correct Answer: Optimizing surface charge, steric coating, and measuring zeta potential under relevant conditions

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com