Eutectic mixtures MCQs With Answer

Eutectic Mixtures MCQs With Answer provide B. Pharm students a focused way to master eutectics—binary systems that exhibit a characteristic eutectic composition and the lowest melting point. Key concepts include melting point depression, binary phase diagrams (liquidus/solidus), eutectic temperature (invariant point), Gibbs phase rule, Raoult’s law, and practical pharmaceutical implications such as liquefaction, incompatibility, solid dispersions, improved dissolution, and topical delivery (e.g., lidocaine–prilocaine). You’ll also see analytical tools (DSC, hot-stage microscopy, XRD), mitigation strategies (adsorbents, coating, granulation), and classic examples (menthol–camphor, thymol–salicylic acid, sulfathiazole–urea). Understanding eutectics during preformulation prevents instability and enables purposeful formulation design. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which best defines a eutectic mixture in pharmaceuticals?

• A single solid phase formed by complete solid solution
• Two solids that form a liquid upon mixing at a specific composition and lowest melting temperature
• A mixture that exhibits a glass transition instead of melting
• An amorphous dispersion stabilized by polymers

Correct Answer: Two solids that form a liquid upon mixing at a specific composition and lowest melting temperature

Q2. In a binary phase diagram, the eutectic point is characterized by:

• Maximum melting temperature of the mixture
• Intersection of two liquidus lines at the lowest temperature
• A single solid phase region at all compositions
• A critical solution temperature

Correct Answer: Intersection of two liquidus lines at the lowest temperature

Q3. The eutectic temperature in a binary eutectic system is:

• Higher than both pure components’ melting points
• Equal to the melting point of the higher-melting component
• Lower than the melting points of both pure components
• Variable with pressure at constant composition

Correct Answer: Lower than the melting points of both pure components

Q4. Which pair is a classic pharmaceutical eutectic that liquefies on trituration?

• Menthol and camphor
• Lactose and starch
• Magnesium stearate and microcrystalline cellulose
• Sucrose and mannitol

Correct Answer: Menthol and camphor

Q5. At the eutectic composition, upon heating, the mixture:

• Melts over a broad temperature range
• Shows a single sharp endotherm at the eutectic temperature
• Exhibits only a glass transition
• Shows no thermal events on DSC

Correct Answer: Shows a single sharp endotherm at the eutectic temperature

Q6. Which statement about phases at the eutectic point (binary system, constant pressure) is correct?

• One phase is present
• Two phases are present
• Three phases coexist (two solids + liquid)
• Four phases coexist

Correct Answer: Three phases coexist (two solids + liquid)

Q7. According to the phase rule at the eutectic point for a binary system (P-T diagram at constant pressure), degrees of freedom (F) are:

• 2
• 1
• 0 (invariant)
• 3

Correct Answer: 0 (invariant)

Q8. Which analytical technique most directly identifies eutectic melting as a low-temperature endotherm?

• Infrared spectroscopy (IR)
• Differential scanning calorimetry (DSC)
• High-performance liquid chromatography (HPLC)
• UV–Visible spectrophotometry

Correct Answer: Differential scanning calorimetry (DSC)

Q9. In preformulation, eutectic formation between a drug and excipient is primarily considered a:

• Chemical degradation pathway
• Microbiological risk
• Physicochemical incompatibility
• Packaging defect

Correct Answer: Physicochemical incompatibility

Q10. Below the eutectic temperature, a binary eutectic mixture at any composition consists of:

• A homogeneous amorphous glass
• A single solid solution phase
• Two distinct solid phases (intimate microcrystalline mixture)
• Only the lower-melting component

Correct Answer: Two distinct solid phases (intimate microcrystalline mixture)

Q11. Which pair forms a pharmaceutical eutectic used to enhance dissolution in classic studies?

• Sulfathiazole and urea
• Ibuprofen and lactose
• Caffeine and starch
• Paracetamol and talc

Correct Answer: Sulfathiazole and urea

Q12. The principal thermodynamic reason for melting point depression in eutectics is:

• Increase in solid-state entropy
• Lowering of the liquid mixture’s chemical potential by mixing
• Decrease in crystal lattice energy of solids
• Increase in vapor pressure of the solids

Correct Answer: Lowering of the liquid mixture’s chemical potential by mixing

Q13. Which topic best estimates the fraction of liquid and solid phases at a given temperature and composition in a binary diagram?

• Lever rule
• Arrhenius equation
• Henderson–Hasselbalch equation
• Stokes’ law

Correct Answer: Lever rule

Q14. A practical sign of eutectic incompatibility during trituration is:

• Powder becomes more free-flowing
• Powder turns to a sticky or oily mass
• No change in appearance
• Immediate color change due to oxidation

Correct Answer: Powder turns to a sticky or oily mass

Q15. Which formulation strategy helps prevent eutectic liquefaction in powders?

• Particle size reduction of both components
• Thorough dry mixing without additives
• Use of adsorbents like light kaolin, talc, or colloidal silica
• Storage at temperatures near the eutectic temperature

Correct Answer: Use of adsorbents like light kaolin, talc, or colloidal silica

Q16. In a simple eutectic of ideal liquids, behavior most closely follows:

• Henry’s law in both components
• Raoult’s law in both components
• Non-ideal activity with strong positive deviation
• Colligative property independence

Correct Answer: Raoult’s law in both components

Q17. Which pair forms a clinically used eutectic mixture that is liquid at room temperature for topical anesthesia?

• Lidocaine and prilocaine
• Lidocaine and epinephrine
• Prilocaine and benzyl alcohol
• Procaine and sucrose

Correct Answer: Lidocaine and prilocaine

Q18. Which statement distinguishes a eutectic mixture from a solid solution?

• Eutectics are a single solid phase; solid solutions are two phases
• Eutectics contain two solid phases below the eutectic temperature; solid solutions are one solid phase
• Both are single phases across all compositions
• Both always show glass transitions

Correct Answer: Eutectics contain two solid phases below the eutectic temperature; solid solutions are one solid phase

Q19. Which experimental method can visually confirm eutectic melting behavior under a microscope?

• Hot-stage microscopy
• Polarimetry
• Flame photometry
• Potentiometry

Correct Answer: Hot-stage microscopy

Q20. The region above the liquidus lines in a binary eutectic phase diagram represents:

• Two solids
• One liquid phase
• One solid phase
• Gas phase

Correct Answer: One liquid phase

Q21. At compositions not equal to the eutectic, melting upon heating typically occurs:

• At a single temperature identical to the eutectic
• Over a temperature range between solidus and liquidus
• Only at the higher-melting component’s temperature
• Without any endothermic event

Correct Answer: Over a temperature range between solidus and liquidus

Q22. Which excipient–drug approach can reduce eutectic risk during mixing?

• Coat one component by wet granulation before blending
• Increase humidity to promote fusion
• Use higher mixing energy and time
• Add plasticizers to both powders

Correct Answer: Coat one component by wet granulation before blending

Q23. Which pair is known to form a eutectic leading to liquefaction in the dispensary?

• Thymol and salicylic acid
• Sucrose and lactose
• Starch and talc
• Calcium carbonate and magnesium oxide

Correct Answer: Thymol and salicylic acid

Q24. Regarding storage, eutectic-prone mixtures should be kept:

• At or above the eutectic temperature
• At lower temperatures and low humidity
• Under vacuum at high temperature
• Exposed to light to prevent liquefaction

Correct Answer: At lower temperatures and low humidity

Q25. Which quick screening test can reveal eutectic incompatibility during preformulation?

• Loss on drying
• Trituration/contact fusion test
• pH solubility profile
• Viscosity measurement

Correct Answer: Trituration/contact fusion test

Q26. What happens when an exact eutectic composition cools from the melt?

• It forms a single crystalline phase
• It solidifies at a constant temperature to two fine crystalline phases
• It vitrifies without crystallization
• It decomposes chemically

Correct Answer: It solidifies at a constant temperature to two fine crystalline phases

Q27. How does particle size reduction influence eutectic liquefaction risk?

• Reduces risk by decreasing contact area
• No effect on risk
• Increases risk by increasing surface contact and intimacy of mixing
• Eliminates risk by stabilizing crystals

Correct Answer: Increases risk by increasing surface contact and intimacy of mixing

Q28. Which statement about deep eutectic solvents (DES) vs simple pharmaceutical eutectics is most accurate?

• DES are always ionic liquids; simple eutectics are always polymers
• DES often involve strong hydrogen-bonding networks; simple eutectics are typically binary melts of small molecules
• DES and simple eutectics are identical in composition and behavior
• Simple eutectics require water; DES do not

Correct Answer: DES often involve strong hydrogen-bonding networks; simple eutectics are typically binary melts of small molecules

Q29. Which pair is notorious for forming a liquid upon mixing due to eutectic behavior?

• Chloral hydrate and camphor
• Sodium chloride and sucrose
• Paracetamol and microcrystalline cellulose
• Mannitol and dicalcium phosphate

Correct Answer: Chloral hydrate and camphor

Q30. In a binary eutectic system, the eutectic composition is best described as the:

• Composition with maximum melting point
• Composition where two liquidus lines meet and the mixture melts at the lowest temperature
• Composition that yields a single solid solution at all temperatures
• Composition independent of components’ interactions

Correct Answer: Composition where two liquidus lines meet and the mixture melts at the lowest temperature

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