Liquid complexes MCQs With Answer

Liquid complexes MCQs With Answer are essential study material for B. Pharm students focusing on drug complexation, solubility enhancement, and formulation design. This introduction covers liquid-phase complexation concepts, inclusion complexes (e.g., cyclodextrins), ion-pairing, coordination complexes, and key characterization techniques like DSC, FTIR, XRD and NMR. Understanding stability constants, phase-solubility diagrams, preparation methods (kneading, co-evaporation, freeze-drying) and factors influencing bioavailability helps students master formulation strategies and analytical evaluation. These targeted MCQs emphasize practical applications, interpretation of data, and problem-solving skills for pharmaceutics exams and research. ‘Now let’s test your knowledge with 50 MCQs on this topic.’

Q1. What is a liquid complex in pharmaceutical sciences?

• A physical mixture of drug and solvent without interaction
• An association between drug and carrier in solution leading to altered properties
• A crystalline solid formed from solvent evaporation
• A suspension of drug particles in liquid

Correct Answer: An association between drug and carrier in solution leading to altered properties

Q2. Which host molecule is most commonly used for inclusion liquid complexes to enhance solubility?

• Polyethylene glycol
• Cyclodextrin
• Sodium lauryl sulfate
• Poloxamer

Correct Answer: Cyclodextrin

Q3. In phase-solubility studies, an AL-type diagram indicates what stoichiometry?

• 1:2 drug:cyclodextrin complex
• 1:1 drug:carrier complex
• No complex formation
• Precipitation of complex

Correct Answer: 1:1 drug:carrier complex

Q4. What does the stability constant (K1:1) measure for a liquid complex?

• The rate of complex formation
• The equilibrium affinity between drug and complexing agent
• The solubility of free drug in water
• The particle size of complex

Correct Answer: The equilibrium affinity between drug and complexing agent

Q5. Which technique is commonly used to confirm inclusion complex formation by observing loss of crystallinity?

• UV-Visible spectroscopy
• X-ray powder diffraction (XRD)
• Conductivity measurement
• pH titration

Correct Answer: X-ray powder diffraction (XRD)

Q6. Which preparation method is preferred for forming liquid inclusion complexes with cyclodextrins?

• Kneading with minimal solvent
• Co-precipitation or co-evaporation in aqueous medium
• Hot-melt extrusion
• Milling dry powders only

Correct Answer: Co-precipitation or co-evaporation in aqueous medium

Q7. A phase-solubility diagram showing AL type with a steep slope suggests what about complexation?

• Very low complexation constant
• High apparent stability constant and improved solubility
• Complex precipitates out of solution
• No interaction between drug and carrier

Correct Answer: High apparent stability constant and improved solubility

Q8. Which spectroscopic change in FTIR suggests molecular interaction in a liquid complex?

• Appearance of a new sharp peak at 3000 cm-1 only
• Shifts or changes in intensity of characteristic functional group bands
• Complete disappearance of all peaks
• No change in spectra

Correct Answer: Shifts or changes in intensity of characteristic functional group bands

Q9. Ion-pairing complexes in solution usually involve which interaction?

• Covalent bonding between drug and carrier
• Electrostatic attraction between oppositely charged ions
• Hydrophobic interactions only
• Hydrogen bonding exclusively

Correct Answer: Electrostatic attraction between oppositely charged ions

Q10. Which analytical method can determine complex stoichiometry in solution using Job’s method?

• Ultraviolet-visible (UV-Vis) spectroscopy
• Thermogravimetric analysis (TGA)
• Scanning electron microscopy (SEM)
• Polarimetry

Correct Answer: Ultraviolet-visible (UV-Vis) spectroscopy

Q11. The Benesi-Hildebrand method is used to calculate what parameter for a 1:1 complex?

• Diffusion coefficient
• Apparent stability constant
• pKa value
• Viscosity of solution

Correct Answer: Apparent stability constant

Q12. Which result indicates successful solubility enhancement after complexation?

• Decreased aqueous solubility compared to free drug
• No change in dissolution rate
• Increased dissolution rate and higher apparent solubility
• Formation of visible precipitate immediately

Correct Answer: Increased dissolution rate and higher apparent solubility

Q13. Inclusion complexation with β-cyclodextrin primarily accommodates which part of a drug molecule?

• Large polar moieties exclusively
• Nonpolar or hydrophobic moieties in the hydrophobic cavity
• Charged groups only
• Entire drug including large polymers

Correct Answer: Nonpolar or hydrophobic moieties in the hydrophobic cavity

Q14. Which thermodynamic parameter indicates whether complexation is enthalpy-driven or entropy-driven?

• pKa
• ΔH and ΔS values
• Viscosity
• Refractive index

Correct Answer: ΔH and ΔS values

Q15. In liquid complexes, which factor can decrease the apparent stability constant?

• Increasing temperature if complexation is exothermic
• Increasing concentration of complexing agent indefinitely
• Using a non-interacting buffer
• Decreasing solvent polarity when complexation favors polar interactions

Correct Answer: Increasing temperature if complexation is exothermic

Q16. Which preparation technique is most suitable to obtain a homogenous liquid complex for poorly water-soluble drugs?

• Direct compression
• Co-solvent dissolution followed by dilution with complexing agent
• Dry sieving
• Cold milling with no solvent

Correct Answer: Co-solvent dissolution followed by dilution with complexing agent

Q17. A BP pharm student observes a disappearance of melting peak in DSC for a complex. This suggests:

• Increased crystallinity of drug
• Conversion to an amorphous or complexed state
• Decomposition of the complexing agent only
• No interaction between components

Correct Answer: Conversion to an amorphous or complexed state

Q18. Which liquid complexation approach can reduce drug irritation and improve taste?

• Ion-pairing to mask charge and taste
• Increasing particle size
• Adding gritty fillers
• Decreasing viscosity only

Correct Answer: Ion-pairing to mask charge and taste

Q19. What is an advantage of using phase-solubility studies for liquid complexes?

• They provide exact molecular structure of complex
• They estimate stoichiometry and apparent stability constants
• They replace the need for spectroscopic confirmation
• They measure particle size distribution

Correct Answer: They estimate stoichiometry and apparent stability constants

Q20. Which molar ratio is typically assumed in analyzing 1:1 complex formation?

• Two drug molecules per carrier
• One drug molecule per one carrier molecule
• Three carrier molecules per drug
• No fixed ratio

Correct Answer: One drug molecule per one carrier molecule

Q21. What does an AP-type phase-solubility diagram indicate?

• Linear increase in solubility with carrier concentration
• Formation of higher-order complexes or precipitation at higher carrier concentrations
• No complex formation
• Immediate drug degradation

Correct Answer: Formation of higher-order complexes or precipitation at higher carrier concentrations

Q22. Which parameter is most directly affected when a drug forms a liquid complex with surfactants?

• Glass transition temperature only
• Micellar solubilization capacity and apparent solubility
• Melting point of surfactant
• Optical rotation

Correct Answer: Micellar solubilization capacity and apparent solubility

Q23. Which NMR observation supports the inclusion of aromatic moiety into cyclodextrin cavity?

• No change in chemical shift
• Upfield shifts of guest proton signals due to shielding
• Complete disappearance of all signals
• Downfield shifts of cyclodextrin protons only

Correct Answer: Upfield shifts of guest proton signals due to shielding

Q24. Which is a limitation of using cyclodextrins for liquid complexes?

• They never improve solubility
• Potentially limited cavity size and cost at high concentrations
• They cause immediate precipitation of drug always
• They are highly hydrophobic and insoluble

Correct Answer: Potentially limited cavity size and cost at high concentrations

Q25. In Benesi-Hildebrand plot for a 1:1 complex, which variables are plotted?

• 1/absorbance vs 1/drug concentration
• 1/(A-A0) vs 1/[host]
• Absorbance vs time
• pH vs solubility

Correct Answer: 1/(A-A0) vs 1/[host]

Q26. Which experimental condition can interfere with accurate determination of stability constant in solution?

• Using a dilute solution within linear range
• Drug degradation during measurement
• Maintaining constant temperature
• Using an inert buffer

Correct Answer: Drug degradation during measurement

Q27. A liquid complex that forms via coordinate bonding usually involves which atom?

• Nonbonding electrons on heteroatoms like O or N coordinating to metal
• Only hydrogen bonding donors
• Pure van der Waals contacts with no specific atom
• Only carbon atoms forming covalent bonds

Correct Answer: Nonbonding electrons on heteroatoms like O or N coordinating to metal

Q28. What does a negative ΔG for complex formation indicate?

• Complexation is non-spontaneous
• Complexation is spontaneous under given conditions
• System is at equilibrium with no complex
• Complex will decompose rapidly

Correct Answer: Complexation is spontaneous under given conditions

Q29. Which method helps evaluate morphology changes upon complexation?

• UV-Vis spectroscopy only
• Scanning electron microscopy (SEM)
• pH measurement
• Melting point apparatus without imaging

Correct Answer: Scanning electron microscopy (SEM)

Q30. In liquid complexation, what role do cosolvents often play?

• They always precipitate the drug
• Increase drug solubility and facilitate interaction with complexing agent
• Reduce chemical stability invariably
• Convert drug to gas

Correct Answer: Increase drug solubility and facilitate interaction with complexing agent

Q31. Which is an indicator of strong host-guest interaction in calorimetric studies?

• Very small heat change
• Significant enthalpy change (ΔH) upon titration
• No change in baseline
• Irreversible precipitation during titration

Correct Answer: Significant enthalpy change (ΔH) upon titration

Q32. What is the effect of complexation on drug permeability across biological membranes?

• Always decreases permeability
• Can increase apparent permeability by enhancing solubility and maintaining supersaturation
• Has no effect on absorption kinetics
• Causes immediate enzymatic degradation

Correct Answer: Can increase apparent permeability by enhancing solubility and maintaining supersaturation

Q33. Which kinetic aspect is important when evaluating liquid complexes for drug release?

• Rate of complex dissociation in biological fluids
• Rate of solid-state crystallization only
• Time to dry the complex powder
• Rate of covalent bond formation

Correct Answer: Rate of complex dissociation in biological fluids

Q34. Which option best describes spectrophotometric titration for complex analysis?

• Monitoring absorbance changes as complexing agent concentration varies
• Measuring melting point changes
• Counting particles under microscope
• Measuring viscosity during stirring

Correct Answer: Monitoring absorbance changes as complexing agent concentration varies

Q35. In a drug–cyclodextrin complex, what does increase in drug chemical stability usually result from?

• Exposure of reactive groups to solvent
• Protection of labile moieties inside the cyclodextrin cavity
• Immediate oxidation by oxygen
• Enhanced hydrolysis rates

Correct Answer: Protection of labile moieties inside the cyclodextrin cavity

Q36. Which formulation challenge can liquid complexes help to overcome?

• Poor solubility and low oral bioavailability of hydrophobic drugs
• Excessive aqueous solubility of all drugs
• Inability to compress tablets due to lack of binder
• High melting point of excipients only

Correct Answer: Poor solubility and low oral bioavailability of hydrophobic drugs

Q37. What does a negative entropy change (ΔS) upon complexation often imply?

• Increased randomness in system
• Decreased degrees of freedom, ordering upon complex formation
• Complete dissociation of solvent molecules
• Temperature-independent binding

Correct Answer: Decreased degrees of freedom, ordering upon complex formation

Q38. Which excipient modification enhances cyclodextrin solubilizing power for liquid complexes?

• Using native α-cyclodextrin only
• Using chemically modified cyclodextrins like HP-β-CD
• Drying the cyclodextrin at high heat only
• Adding ionic salts to precipitate cyclodextrin

Correct Answer: Using chemically modified cyclodextrins like HP-β-CD

Q39. Which observation during dilution of a concentrated complex solution suggests weak complexation?

• No change in free drug concentration
• Rapid increase in free drug concentration due to dissociation
• Complete precipitation of complexing agent
• Formation of a gel instantly

Correct Answer: Rapid increase in free drug concentration due to dissociation

Q40. Which parameter is important when designing liquid complex dosage forms for parenteral use?

• Osmolarity and stability of complex in aqueous medium
• Tablet disintegration time
• Compression strength only
• Color of the powder

Correct Answer: Osmolarity and stability of complex in aqueous medium

Q41. Which metric quantifies fold-increase in solubility due to complexation?

• Partition coefficient
• Solubility enhancement factor (SE)
• Melting point depression
• Viscosity index

Correct Answer: Solubility enhancement factor (SE)

Q42. For an amphiphilic drug, which complexation approach can improve micellar solubilization in liquids?

• Complexation with polystyrene
• Use of surfactants to form micelle-drug complexes
• Lyophilization without surfactant
• Dry granulation with no water

Correct Answer: Use of surfactants to form micelle-drug complexes

Q43. Which experimental evidence best distinguishes between simple solubilization and true host–guest inclusion?

• Only increased turbidity
• Specific spectroscopic shifts (NMR/FTIR) and changes in thermograms
• Identical XRD peaks as free drug
• Only visual color change

Correct Answer: Specific spectroscopic shifts (NMR/FTIR) and changes in thermograms

Q44. What is the main reason for performing solubility-pH profiling during complexation studies?

• To determine tablet hardness
• To understand the influence of ionization on complex stability and solubility
• To measure viscosity changes only
• To assess melting point variations

Correct Answer: To understand the influence of ionization on complex stability and solubility

Q45. Which complexation assessment uses dilution and measurement of free drug concentration to obtain binding parameters?

• Dialysis or equilibrium dialysis methods
• Direct optical microscopy
• High-speed centrifugation only
• Bulk density measurement

Correct Answer: Dialysis or equilibrium dialysis methods

Q46. Which effect is commonly observed when a drug forms a stable liquid complex with a metal ion?

• Increased volatility of drug
• Altered UV-Vis absorbance and possible coloration due to coordination
• Complete insolubility in all solvents
• Instant polymerization

Correct Answer: Altered UV-Vis absorbance and possible coloration due to coordination

Q47. For evaluation of complex in biological media, which factor must be considered?

• Compatibility with buffers, competing endogenous ligands, and dilution effects in vivo
• Only the color of formulation
• Tablet friability
• Melting point of excipients exclusively

Correct Answer: Compatibility with buffers, competing endogenous ligands, and dilution effects in vivo

Q48. What is the primary goal of forming liquid complexes in topical formulations?

• Reduce skin permeation
• Enhance drug solubility and penetration through skin layers
• Increase formulation odour only
• Convert drug to inert salt with no activity

Correct Answer: Enhance drug solubility and penetration through skin layers

Q49. Which quality attribute should be monitored during scale-up of liquid complex production?

• Consistency of complexation efficiency and stability across batches
• Only the label design
• Tablet breaking force
• Color of the shipping box

Correct Answer: Consistency of complexation efficiency and stability across batches

Q50. Which statement reflects best practice when reporting MCQ answers for liquid complexes in academic exams?

• Provide vague answers without justification
• Report the exact option text and, where required, a concise rationale or reference to data
• List only numerical values without context
• Avoid indicating the correct option clearly

Correct Answer: Report the exact option text and, where required, a concise rationale or reference to data

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