Eutectic mixtures MCQs With Answer

Eutectic mixtures MCQs With Answer are essential study material for B. Pharm students learning pharmaceutics, physical chemistry, and dosage-form design. This introduction explains eutectic systems, eutectic point, phase behavior, melting point depression, and pharmaceutical relevance such as topical eutectic formulations and deep eutectic solvents for improved solubility and drug delivery. You will learn how eutectic mixtures form, how to read binary phase diagrams, detect eutectics using DSC and microscopy, and how eutectic behavior affects stability, compaction, and dissolution. Mastering these concepts helps in rational excipient selection and formulation troubleshooting. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is a eutectic mixture in pharmaceutical context?

• A homogeneous single-phase solution with one melting point
• A crystalline mixture where components solidify simultaneously at the lowest melting temperature
• A supersaturated amorphous solid with high glass transition temperature
• An ionic salt formed by acid-base reaction

Correct Answer: A crystalline mixture where components solidify simultaneously at the lowest melting temperature

Q2. What does the eutectic point represent on a binary phase diagram?

• The composition where one component sublimes directly to vapor
• The highest temperature at which a single liquid coexists with two solids
• The lowest temperature where the liquid phase coexists with two solid phases
• The temperature where both components have equal vapor pressures

Correct Answer: The lowest temperature where the liquid phase coexists with two solid phases

Q3. Which reaction best describes the eutectic transformation on cooling?

• L -> alpha + beta
• alpha -> L + beta
• L -> alpha
• beta -> L + alpha

Correct Answer: L -> alpha + beta

Q4. Which analytical technique is most commonly used to identify eutectic formation through melting endotherms?

• High performance liquid chromatography (HPLC)
• Differential scanning calorimetry (DSC)
• Infrared spectroscopy (FTIR)
• Gas chromatography (GC)

Correct Answer: Differential scanning calorimetry (DSC)

Q5. How does a eutectic mixture typically affect melting point compared with pure components?

• The eutectic always has a higher melting point than both components
• The eutectic has a melting point equal to the average of both components
• The eutectic has a lower melting point than either pure component
• Melting point is not changed by eutectic formation

Correct Answer: The eutectic has a lower melting point than either pure component

Q6. Which of the following is a known pharmaceutical eutectic pair used in topical formulations?

• Paracetamol and ibuprofen
• Lidocaine and prilocaine
• Aspirin and metformin
• Amoxicillin and clavulanic acid

Correct Answer: Lidocaine and prilocaine

Q7. What microstructure is commonly observed in eutectic solids formed by two immiscible crystalline phases?

• Porous spherical agglomerates
• Lamellar or rod-like alternating phases
• Completely amorphous matrix without features
• Single large crystal of mixed composition

Correct Answer: Lamellar or rod-like alternating phases

Q8. How does eutectic formation influence tablet manufacturing if one component liquefies at formulation temperature?

• Improves powder flow and always enhances compaction
• Can cause sticking, poor flow, and challenges during compression
• Makes the blend chemically inert and stable
• Prevents any dissolution of the drug in biological fluids

Correct Answer: Can cause sticking, poor flow, and challenges during compression

Q9. Which statement distinguishes a eutectic from a solid solution?

• Both are identical; there is no difference
• A eutectic consists of two distinct crystalline phases coexisting, while a solid solution is a single phase with one component substituted into the crystal lattice of the other
• A solid solution always has a lower melting point than eutectic
• A eutectic is always amorphous while solid solutions are crystalline

Correct Answer: A eutectic consists of two distinct crystalline phases coexisting, while a solid solution is a single phase with one component substituted into the crystal lattice of the other

Q10. What practical advantage do deep eutectic solvents (DES) offer in pharmaceutics?

• They increase vapor pressure to enhance inhalation delivery
• They provide tunable solubilization and can enhance drug permeability and stability
• They always convert drugs into crystalline forms
• They are used to polymerize monomers in tablet coatings

Correct Answer: They provide tunable solubilization and can enhance drug permeability and stability

Q11. In a binary phase diagram, how does the lever rule help the formulator?

• To calculate molecular weight of components
• To estimate proportions of solid phases and liquid at a given temperature and composition
• To determine pH of the mixture
• To identify chemical reactivity between components

Correct Answer: To estimate proportions of solid phases and liquid at a given temperature and composition

Q12. Which phenomenon is commonly used to detect microstructural lamellae in eutectic solids?

• Scanning electron microscopy (SEM)
• Nuclear magnetic resonance (NMR)
• Ultraviolet-visible spectroscopy (UV-Vis)
• Polarimetry

Correct Answer: Scanning electron microscopy (SEM)

Q13. What happens to solubility of a poorly water-soluble drug when converted into a eutectic with a hydrophilic coformer?

• Solubility always decreases
• Solubility can increase due to enhanced wettability and reduced melting point
• Solubility remains unchanged because crystals are unaffected
• Solubility becomes zero due to complexation

Correct Answer: Solubility can increase due to enhanced wettability and reduced melting point

Q14. How does cooling rate affect eutectic microstructure during solidification?

• Faster cooling typically produces finer lamellar spacing
• Cooling rate has no effect on microstructure
• Slower cooling always leads to amorphous solids
• Faster cooling leads to larger, well-formed single crystals

Correct Answer: Faster cooling typically produces finer lamellar spacing

Q15. Which thermodynamic principle explains the melting point depression in eutectic mixtures?

• Raoult’s law and Gibbs free energy minimization for mixing
• Le Chatelier’s principle for pressure changes
• Boiling point elevation due to solutes
• Henderson-Hasselbalch equation

Correct Answer: Raoult’s law and Gibbs free energy minimization for mixing

Q16. What characterization technique distinguishes two crystalline phases in a eutectic solid?

• X-ray powder diffraction (XRPD)
• Mass spectrometry (MS)
• Liquid chromatography (LC)
• pH titration

Correct Answer: X-ray powder diffraction (XRPD)

Q17. Which is a potential drawback of unintended eutectic formation in a mixed-drug tablet?

• Enhanced chemical stability of active ingredients
• Unexpected liquefaction during storage causing dosage inaccuracy
• Guaranteed improved bioavailability
• Complete prevention of moisture uptake

Correct Answer: Unexpected liquefaction during storage causing dosage inaccuracy

Q18. What is a ternary eutectic?

• A mixture of three components that exhibits a eutectic point involving three solid phases and liquid coexistence at a lowest temperature
• A binary system with a third impurity ignored
• A mixture that forms an only amorphous glass
• A two-component solid solution with one impurity

Correct Answer: A mixture of three components that exhibits a eutectic point involving three solid phases and liquid coexistence at a lowest temperature

Q19. Which of the following is true for congruent melting compounds compared to eutectic mixtures?

• Congruent melting compounds melt at a single temperature without decomposition to other solid phases
• They always form eutectic lamellae when cooled
• They decompose into multiple solid phases upon melting
• They cannot be used in pharmaceutical formulations

Correct Answer: Congruent melting compounds melt at a single temperature without decomposition to other solid phases

Q20. Which formulation strategy intentionally uses eutectic formation to lower melting point and enhance transdermal delivery?

• Microencapsulation
• Use of eutectic mixture of local anesthetics (e.g., lidocaine-prilocaine) for topical penetration
• Enteric coating
• Spray drying to form stable hydrates

Correct Answer: Use of eutectic mixture of local anesthetics (e.g., lidocaine-prilocaine) for topical penetration

Q21. Which is NOT a typical method to prevent undesired eutectic liquefaction in formulations?

• Use of absorbent excipients to sequester melt
• Formulation at compositions away from eutectic point
• Control of storage temperature below eutectic point
• Addition of more of the eutectic-forming pair to reach eutectic composition

Correct Answer: Addition of more of the eutectic-forming pair to reach eutectic composition

Q22. How does particle size reduction influence eutectic behavior of a drug-excipient mixture?

• Smaller particles increase contact area and can promote eutectic formation and faster melting
• Particle size has no influence on eutectic formation
• Larger particles always form eutectics more readily
• Particle size only affects vapor pressure, not eutectic behavior

Correct Answer: Smaller particles increase contact area and can promote eutectic formation and faster melting

Q23. Which statement describes a peritectic reaction, distinguishing it from a eutectic reaction?

• Peritectic is L -> alpha + beta; eutectic is L + alpha -> beta
• Peritectic is L + alpha -> beta on cooling; eutectic is L -> alpha + beta
• Peritectic and eutectic are identical phenomena
• Peritectic only occurs in gases

Correct Answer: Peritectic is L + alpha -> beta on cooling; eutectic is L -> alpha + beta

Q24. What role do eutectics play in solid dispersions for poorly soluble drugs?

• They always stabilize the crystalline drug and reduce dissolution
• They can lower melting point and increase wettability, potentially improving dissolution rate
• They prevent any solid-state interaction between drug and polymer
• They are not relevant to solid dispersions

Correct Answer: They can lower melting point and increase wettability, potentially improving dissolution rate

Q25. If two pharmaceutical solids are completely miscible in the liquid state but immiscible in the solid state, what binary feature is likely?

• Formation of a continuous solid solution across compositions
• A eutectic system with two distinct solid phases at lower temperatures
• Immediate chemical reaction to form a new compound
• No interaction and independent melting points only

Correct Answer: A eutectic system with two distinct solid phases at lower temperatures

Q26. Which property change is MOST likely when a drug forms a eutectic with a low-melting coformer?

• Increase in melting point and decreased dissolution
• Decrease in melting point and possible liquefaction at room temperature
• Complete chemical transformation to a new covalent compound
• No change in thermal behavior

Correct Answer: Decrease in melting point and possible liquefaction at room temperature

Q27. In DSC, how does a eutectic melting event typically appear?

• As a single sharp endotherm at the eutectic temperature followed by separate higher-temperature endotherms for pure component melting
• Only as exotherms with no endotherms
• As multiple small endotherms with no clear eutectic peak
• As a baseline shift with no peaks

Correct Answer: As a single sharp endotherm at the eutectic temperature followed by separate higher-temperature endotherms for pure component melting

Q28. Which concept explains why eutectic mixtures can have enhanced dissolution rates?

• Higher crystallinity reduces surface area
• Lower melting point increases molecular mobility and wettability at the solid-liquid interface
• Eutectics always form insoluble salts
• Because eutectics are magnetic they mix better in dissolution media

Correct Answer: Lower melting point increases molecular mobility and wettability at the solid-liquid interface

Q29. How can X-ray diffraction patterns change when two drugs form a eutectic mixture without chemical reaction?

• XRPD will show disappearance of both phase peaks and a single new amorphous halo
• XRPD will display peaks corresponding to both crystalline phases, possibly with altered intensities but not new covalent-phase peaks
• XRPD becomes useless for eutectic analysis
• XRPD will show only solvent peaks

Correct Answer: XRPD will display peaks corresponding to both crystalline phases, possibly with altered intensities but not new covalent-phase peaks

Q30. Which excipient characteristic is most helpful to avoid eutectic liquefaction in a heat-sensitive formulation?

• Excipient with melting point close to eutectic temperature
• Excipient that absorbs released liquid or increases solid matrix viscosity (e.g., silica)
• Excipient that forms low-melting eutectics with the API
• Excipient that is volatile at storage conditions

Correct Answer: Excipient that absorbs released liquid or increases solid matrix viscosity (e.g., silica)

Q31. What does incongruent melting mean in the context of binary pharmaceutical systems?

• The compound melts and forms a liquid of identical composition to the solid
• On melting, the compound decomposes or reacts to form a liquid of different composition and a new solid phase
• The compound sublimes without melting
• The compound remains solid at all temperatures

Correct Answer: On melting, the compound decomposes or reacts to form a liquid of different composition and a new solid phase

Q32. Which of the following is an advantage of intentionally designing a eutectic for a topical anesthetic?

• Increases melting point to prevent skin absorption
• Generates local liquid phase at skin temperature enhancing partitioning into stratum corneum
• Eliminates drug potency
• Makes the product more acidic only

Correct Answer: Generates local liquid phase at skin temperature enhancing partitioning into stratum corneum

Q33. How does humidity affect eutectic mixtures composed of hygroscopic components?

• Humidity has no effect on eutectics
• Absorbed moisture can plasticize the mixture, lower the solidus, and promote liquefaction or crystallization changes
• Humidity always crystallizes eutectics into a single phase
• Humidity converts eutectics into salts immediately

Correct Answer: Absorbed moisture can plasticize the mixture, lower the solidus, and promote liquefaction or crystallization changes

Q34. Which property is most useful to screen for eutectic-forming potential between an API and excipient?

• Similar color and odor
• Thermal analysis data (melting points, DSC) and miscibility information
• Solubility in hexane only
• Viscosity of the pure components

Correct Answer: Thermal analysis data (melting points, DSC) and miscibility information

Q35. In formulation development, why might a formulator intentionally avoid the eutectic composition?

• Because eutectic composition guarantees maximum stability
• Because eutectic composition often produces the lowest melting point and potential handling/storage issues
• Avoidance is pointless; eutectic always enhances manufacturability
• Because eutectic compositions are illegal

Correct Answer: Because eutectic composition often produces the lowest melting point and potential handling/storage issues

Q36. Which term describes the lowest temperature at which only liquid exists when heating a eutectic mixture?

• Solidus
• Liquidus
• Eutectic temperature
• Glass transition temperature

Correct Answer: Eutectic temperature

Q37. What is the relationship between eutectic composition and component proportions?

• Eutectic composition is a specific mole or weight fraction where melting point is lowest for the binary system
• Eutectic composition is always 50:50 by weight
• Eutectic composition is arbitrary and has no physical meaning
• Eutectic composition equals the higher melting component concentration only

Correct Answer: Eutectic composition is a specific mole or weight fraction where melting point is lowest for the binary system

Q38. Which processing technique could unintentionally produce eutectic zones due to localized heating?

• Cold compression at sub-zero temperatures
• High shear melt processing or hot-melt extrusion
• Lyophilization at very low temperatures
• Supercritical CO2 drying without heat

Correct Answer: High shear melt processing or hot-melt extrusion

Q39. Which of the following is true about eutectic liquids formed on partial melting of a binary mixture?

• The liquid has the same composition as the original solid mixture at all temperatures
• The liquid composition corresponds to the liquidus at that temperature and can differ from the original overall composition
• Liquid formed is always pure solvent
• Partial melting cannot form a liquid phase in eutectics

Correct Answer: The liquid composition corresponds to the liquidus at that temperature and can differ from the original overall composition

Q40. Which factor does NOT influence the eutectic temperature of a binary system?

• Intermolecular interactions between components
• Atmospheric pressure (within normal ranges it has minimal effect but extreme pressures can affect phase behavior)
• Impurity levels
• Color of one component

Correct Answer: Color of one component

Q41. How can formulators exploit eutectic behavior to design rapidly dissolving oral granules?

• By selecting coformers that form high-melting eutectics to slow dissolution
• By choosing hydrophilic coformers that produce lower-melting eutectics to improve wettability and dissolution
• By ensuring products remain highly crystalline and non-wettable
• By avoiding any mixing of API with excipients

Correct Answer: By choosing hydrophilic coformers that produce lower-melting eutectics to improve wettability and dissolution

Q42. Which term describes the temperature below which solid phases begin to form on cooling?

• Liquidus
• Solidus
• Tg (glass transition)
• Boiling point

Correct Answer: Solidus

Q43. Which experimental observation would most strongly indicate eutectic formation between two drugs?

• Single melting endotherm equal to the melting point of one pure drug only
• A new sharp endotherm at a temperature lower than both melting points, plus residual peaks for each component
• Complete loss of any thermal events on DSC
• No changes in microscopy images

Correct Answer: A new sharp endotherm at a temperature lower than both melting points, plus residual peaks for each component

Q44. Which of the following is an appropriate formulation approach if two actives form an undesirable eutectic?

• Blend them at the eutectic composition intentionally
• Use physical separation strategies (e.g., layered tablets, separate granules) or choose alternative excipients
• Increase storage temperature above melting point
• Remove both actives from the formulation

Correct Answer: Use physical separation strategies (e.g., layered tablets, separate granules) or choose alternative excipients

Q45. What effect does forming a eutectic have on the melting enthalpy (ΔH) measured by DSC?

• There is no enthalpy associated with eutectic melting
• A distinct endothermic peak with an enthalpy proportional to the amount of eutectic liquid formed appears
• Only exothermic peaks are observed
• ΔH always doubles compared to pure components

Correct Answer: A distinct endothermic peak with an enthalpy proportional to the amount of eutectic liquid formed appears

Q46. Which formulation attribute may be improved by using a eutectic adjuvant in topical creams?

• Reduced skin permeation due to higher crystallinity
• Increased drug partitioning into skin due to localized melting and enhanced solubilization
• Complete elimination of local irritation always
• Increased systemic toxicity always

Correct Answer: Increased drug partitioning into skin due to localized melting and enhanced solubilization

Q47. Which statement about eutectic versus cocrystal formation is correct?

• Eutectics result from chemical bonding between components, while cocrystals are simple mixtures
• Cocrystals are new crystalline phases with defined stoichiometry, while eutectics are intimate mixtures of two separate crystalline phases
• Both are identical in structure and thermal behavior
• Eutectics cannot be formed by pharmaceutically acceptable coformers

Correct Answer: Cocrystals are new crystalline phases with defined stoichiometry, while eutectics are intimate mixtures of two separate crystalline phases

Q48. Which factor is LEAST likely to promote eutectic formation between two solids?

• Strong intermolecular attraction and partial miscibility in liquid state
• Good molecular complementarity that discourages chemical reaction
• Extremely high immiscibility in liquid state with no interaction
• Fine particle contact and mechanical mixing

Correct Answer: Extremely high immiscibility in liquid state with no interaction

Q49. Why is knowledge of eutectic behavior important for stability testing of solid dosage forms?

• It is not relevant to stability testing
• Because eutectic formation can lead to phase changes, liquefaction, or altered dissolution during storage and stress conditions
• Because eutectics always prevent degradation under all conditions
• Because eutectics convert solids into pure gases

Correct Answer: Because eutectic formation can lead to phase changes, liquefaction, or altered dissolution during storage and stress conditions

Q50. Which practical test can a formulator perform early in development to screen for potential eutectic problems?

• Short thermal scan (DSC) and small-scale hot-tablet or hot-stage microscopy to observe melting and liquefaction behavior
• Only viscosity measurements at infinite dilution
• Colorimetric assay for impurities only
• Gas chromatography for non-volatile impurities only

Correct Answer: Short thermal scan (DSC) and small-scale hot-tablet or hot-stage microscopy to observe melting and liquefaction behavior

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