Binary solutions MCQs With Answer

Mastering Binary solutions MCQs With Answer is essential for B.Pharm students studying physical pharmacy and formulation science. This concise collection focuses on binary solutions, covering Raoult’s law, ideal and non‑ideal behavior, activity coefficients, azeotropes, vapor‑liquid equilibrium, partial molar properties, and pharmaceutical solvent systems. Questions emphasize calculation concepts, phase diagrams, colligative effects and applications like cosolvent selection and distillation of solvent mixtures. Clear explanations and varied difficulty levels help strengthen exam preparedness and practical understanding of solvent interactions in drug formulation. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What defines a binary solution in pharmaceutical context?

• A mixture of three components with one solvent and two solutes
• A solution consisting of two chemical species only
• An emulsion containing two phases
• A colloidal system with two particle sizes

Correct Answer: A solution consisting of two chemical species only

Q2. Which law describes the vapor pressure of each volatile component in an ideal binary solution?

• Henry’s law
• Raoult’s law
• Gibbs-Duhem equation
• Van’t Hoff law

Correct Answer: Raoult’s law

Q3. In an ideal binary solution, how does the total vapor pressure relate to mole fractions?

• It is independent of mole fractions
• It equals the product of mole fractions
• It equals the sum of the partial pressures each proportional to mole fractions
• It equals the difference of the pure component vapor pressures

Correct Answer: It equals the sum of the partial pressures each proportional to mole fractions

Q4. What does a positive deviation from Raoult’s law indicate?

• Stronger attraction between unlike molecules than like molecules
• Weaker attraction between unlike molecules leading to higher vapor pressure
• Formation of a stable azeotrope with lower boiling point
• Complete immiscibility of components

Correct Answer: Weaker attraction between unlike molecules leading to higher vapor pressure

Q5. Which phenomenon in binary solutions results when vapor and liquid have the same composition at a given temperature?

• Eutectic point
• Azeotrope
• Glass transition
• Sublimation

Correct Answer: Azeotrope

Q6. A negative deviation from Raoult’s law commonly leads to which of the following?

• Higher total vapor pressure than predicted
• Lower total vapor pressure and possible minimum boiling azeotrope
• Complete phase separation
• Increased volatility of both components equally

Correct Answer: Lower total vapor pressure and possible minimum boiling azeotrope

Q7. What is the primary use of binary solvent systems in pharmaceutical formulation?

• To reduce melting point of active ingredients
• To adjust drug solubility, extraction efficiency, and processing behavior
• To create colloidal suspensions only
• To prevent any solute dissolution

Correct Answer: To adjust drug solubility, extraction efficiency, and processing behavior

Q8. In a binary solution where component B is nonvolatile, which rule applies to the solvent vapor pressure?

• Vapor pressure equals pure B vapor pressure
• Raoult’s law for solvent A only
• Henry’s law for solvent A
• Gibbs phase rule exclusively

Correct Answer: Raoult’s law for solvent A only

Q9. Which parameter expresses the deviation of a real solution from ideality?

• Relative volatility
• Activity coefficient
• Boiling point elevation constant
• Viscosity index

Correct Answer: Activity coefficient

Q10. The Gibbs-Duhem equation in binary systems relates changes in which quantities?

• Temperature and pressure only
• Chemical potentials (or activities) of the two components
• Viscosity and surface tension
• Boiling point and freezing point

Correct Answer: Chemical potentials (or activities) of the two components

Q11. What is relative volatility important for in binary distillation?

• Calculating solubility in cosolvents
• Determining ease of separation by distillation
• Predicting osmotic pressure
• Estimating drug partition coefficient

Correct Answer: Determining ease of separation by distillation

Q12. In a binary phase diagram (temperature vs composition), what does the bubble point curve represent?

• Temperature where the first bubble of vapor forms from liquid
• Temperature where the last drop of liquid evaporates
• Temperature of maximum miscibility
• Temperature of crystallization onset

Correct Answer: Temperature where the first bubble of vapor forms from liquid

Q13. For dilute binary solutions with a volatile solute at low concentration, which law often applies to the solute’s vapor pressure?

• Raoult’s law exactly
• Henry’s law
• Gibbs adsorption law
• Dalton’s law

Correct Answer: Henry’s law

Q14. Partial molar volume in a binary mixture is useful for understanding:

• Electrical conductivity changes
• Volume change upon mixing and molecular interactions
• Color changes during mixing
• Magnetic susceptibility

Correct Answer: Volume change upon mixing and molecular interactions

Q15. Which statement about ideal binary solutions is true?

• Interactions between unlike molecules equal interactions between like molecules
• Unlike molecules never interact
• They always form azeotropes
• Activity coefficients vary widely with composition

Correct Answer: Interactions between unlike molecules equal interactions between like molecules

Q16. How does adding a nonvolatile solute to a solvent in a binary solution affect the solvent’s vapor pressure?

• Increases the vapor pressure
• Decreases the vapor pressure (vapor pressure lowering)
• No change in vapor pressure
• Causes immediate boiling

Correct Answer: Decreases the vapor pressure (vapor pressure lowering)

Q17. The boiling point elevation in a binary solution is a colligative property that depends primarily on:

• The identity of the solute molecules
• The number of solute particles relative to solvent molecules
• The color of the solute
• The vapor pressure of pure solute

Correct Answer: The number of solute particles relative to solvent molecules

Q18. Which binary mixture is likely to form a minimum-boiling azeotrope?

• Components with strong attractive interactions
• Components with weaker interactions than pure components
• Completely immiscible liquids
• Two salts in aqueous solution

Correct Answer: Components with weaker interactions than pure components

Q19. In pharmaceutical extraction, why are binary solvent mixtures often preferred to single solvents?

• They always produce azeotropes for easy distillation
• They allow tuning of polarity and selectivity for target drug extraction
• They eliminate the need for drying agents
• They reduce the boiling point to room temperature

Correct Answer: They allow tuning of polarity and selectivity for target drug extraction

Q20. What does the term “miscibility” mean for two liquids forming a binary solution?

• They react chemically to form a new compound
• They mix in all proportions to form a homogeneous phase
• They form a suspension
• They form a covalent bond network

Correct Answer: They mix in all proportions to form a homogeneous phase

Q21. Which equation links vapor-phase composition and liquid-phase composition for ideal mixtures?

• Raoult’s law combined with Dalton’s law
• Henry-Dalton equation
• Van’t Hoff equation
• Arrhenius equation

Correct Answer: Raoult’s law combined with Dalton’s law

Q22. What is the significance of activity in binary solutions?

• It equals the mole fraction always
• It corrects concentration for non-ideal behavior and replaces effective concentration in thermodynamics
• It measures kinetic stability only
• It is irrelevant for vapor-liquid equilibrium

Correct Answer: It corrects concentration for non-ideal behavior and replaces effective concentration in thermodynamics

Q23. Which of the following best describes a maximum-boiling azeotrope?

• It boils at a lower temperature than both pure components
• It boils at a higher temperature than either pure component
• It cannot be separated by distillation
• It only forms in solid mixtures

Correct Answer: It boils at a higher temperature than either pure component

Q24. In terms of formulation, why is knowledge of partial molar quantities useful?

• To design dissolution media with desired volume and density changes upon mixing
• To measure optical rotation
• To predict color stability of drugs
• To determine magnetic resonance properties

Correct Answer: To design dissolution media with desired volume and density changes upon mixing

Q25. Dalton’s law is used in binary vapor mixtures to relate:

• Total pressure to the sum of partial pressures of each gas
• Activity coefficients to mole fractions
• Boiling point to composition directly
• Freezing point to osmotic pressure

Correct Answer: Total pressure to the sum of partial pressures of each gas

Q26. Which experimental method helps determine activity coefficients in binary liquid mixtures?

• Calorimetry only
• Vapor pressure measurements and boiling point data
• Spectrophotometry exclusively
• Microscopy

Correct Answer: Vapor pressure measurements and boiling point data

Q27. What is the lever rule used for in binary phase diagrams?

• Calculating activity coefficients
• Determining proportion of phases at equilibrium from a given overall composition
• Estimating vapor pressures from boiling points
• Predicting azeotrope formation

Correct Answer: Determining proportion of phases at equilibrium from a given overall composition

Q28. Which effect describes the lowering of freezing point when a solute is added to a solvent in a binary solution?

• Boiling point elevation
• Freezing point depression
• Osmotic pressure reduction
• Vapor pressure inversion

Correct Answer: Freezing point depression

Q29. For a binary mixture of ethanol and water, which statement is true regarding distillation?

• They separate completely by simple distillation at any composition
• They form an azeotrope near 95.6% ethanol that limits purity by simple distillation
• Ethanol is nonvolatile so it cannot be distilled
• Water and ethanol are immiscible and form two layers

Correct Answer: They form an azeotrope near 95.6% ethanol that limits purity by simple distillation

Q30. What happens to the activity coefficient of a solute as a binary mixture approaches ideality?

• It approaches zero
• It approaches one
• It becomes negative
• It becomes infinite

Correct Answer: It approaches one

Q31. Which pharmaceutical process must consider binary azeotropes to avoid undesired composition during solvent removal?

• Lyophilization
• Vacuum distillation and rotary evaporation
• Sterile filtration
• Tablet compression

Correct Answer: Vacuum distillation and rotary evaporation

Q32. In binary liquid mixtures, what does excess Gibbs energy quantify?

• Deviation of the mixture’s Gibbs free energy from ideal behavior
• Total Gibbs energy of pure components only
• Entropy change on mixing only
• Boiling point difference between components

Correct Answer: Deviation of the mixture’s Gibbs free energy from ideal behavior

Q33. Which term best describes a solvent pair chosen to maximize solubility of a poorly soluble drug?

• Immiscible blend
• Cosolvent system
• Buffer solution
• Suspending medium

Correct Answer: Cosolvent system

Q34. What is the effect of adding a volatile cosolvent to water on the overall vapor pressure of the binary mixture?

• The total vapor pressure is the sum of partial pressures determined by each component’s mole fraction
• It always reduces the total vapor pressure to zero
• It equals the vapor pressure of pure water only
• It makes the mixture nonvolatile

Correct Answer: The total vapor pressure is the sum of partial pressures determined by each component’s mole fraction

Q35. When designing a formulation, why is knowledge of binary solvent polarity important?

• Polarity affects solubility, partitioning, and stability of drug molecules
• Polarity determines tablet hardness only
• Polarity causes chemical reactions always
• Polarity has no role in extraction processes

Correct Answer: Polarity affects solubility, partitioning, and stability of drug molecules

Q36. Which of these is NOT a colligative property relevant to binary solutions with nonvolatile solute?

• Boiling point elevation
• Freezing point depression
• Osmotic pressure
• Surface tension reduction due to surfactants

Correct Answer: Surface tension reduction due to surfactants

Q37. In a binary vapor-liquid equilibrium, which composition is richer in the more volatile component?

• The liquid phase at the bubble point
• The vapor phase in equilibrium with the liquid
• Both phases have identical composition always
• The solid phase

Correct Answer: The vapor phase in equilibrium with the liquid

Q38. What role does temperature play in the vapor-liquid equilibrium of a binary solution?

• Temperature has no effect on equilibrium compositions
• Temperature shifts vapor and liquid compositions and can change azeotrope behavior
• Temperature only affects solids
• Temperature fixes the activity coefficients to unity

Correct Answer: Temperature shifts vapor and liquid compositions and can change azeotrope behavior

Q39. Which binary mixture behavior requires non-ideal solution models like Wilson, NRTL, or UNIQUAC?

• When activity coefficients deviate significantly from unity due to molecular interactions
• For perfectly ideal solutions only
• For dilute electrolyte solutions exclusively
• When components are isotopes

Correct Answer: When activity coefficients deviate significantly from unity due to molecular interactions

Q40. How is the mole fraction of component A in a binary solution defined?

• Moles of B divided by total moles
• Moles of A divided by total moles of A and B
• Mass of A divided by mass of B
• Volume of A divided by volume of mixture

Correct Answer: Moles of A divided by total moles of A and B

Q41. What is an important safety consideration when distilling binary solvent mixtures in the lab?

• Binary mixtures never form flammable vapors
• Formation of azeotropes can create vapors with unexpected boiling points and flammability
• Binary mixtures always reduce explosion risk
• There is no need for ventilation

Correct Answer: Formation of azeotropes can create vapors with unexpected boiling points and flammability

Q42. In pharmaceutical analysis, why measure vapor pressure of a binary mixture?

• To determine pH of the solution
• To infer activity coefficients and predict separation behavior
• To calculate tablet dissolution rate directly
• To measure optical density

Correct Answer: To infer activity coefficients and predict separation behavior

Q43. Which of the following best describes an ideal binary solution’s excess enthalpy?

• Positive and large
• Zero
• Negative and large
• Infinite

Correct Answer: Zero

Q44. What is the expected effect on solubility when mixing two solvents with complementary polarity in a binary cosolvent system?

• Solubility is always reduced
• Solubility can be enhanced by tuning overall polarity to match solute
• Solubility becomes independent of solvent composition
• Solubility is only affected by temperature

Correct Answer: Solubility can be enhanced by tuning overall polarity to match solute

Q45. Which of the following is a direct consequence of Raoult’s law for an ideal binary mixture of two volatile liquids?

• Partial pressure of each component equals its pure vapor pressure
• Partial pressure of each component equals its mole fraction times its pure vapor pressure
• Total pressure equals product of pure vapor pressures
• Activity coefficients are always zero

Correct Answer: Partial pressure of each component equals its mole fraction times its pure vapor pressure

Q46. What does a convex (positive) excess Gibbs energy curve vs composition indicate about interactions?

• Stronger unlike interactions than like interactions
• Weaker unlike interactions and tendency toward positive deviation from ideality
• Complete chemical reaction between components
• Perfect ideality

Correct Answer: Weaker unlike interactions and tendency toward positive deviation from ideality

Q47. In binary solvent selection for topical formulation, why consider binary solution properties?

• To ensure solvents are immiscible with skin lipids
• To optimize solvent penetration, drug solubility, and evaporation rate
• Because single solvents are illegal
• To maximize color vibrancy

Correct Answer: To optimize solvent penetration, drug solubility, and evaporation rate

Q48. If component A has a much higher vapor pressure than B at a given temperature, the vapor in equilibrium will be:

• Richer in component B
• Richer in component A
• Equal composition to the liquid always
• Nonvolatile

Correct Answer: Richer in component A

Q49. Which measurement can directly show formation of azeotrope during binary distillation?

• Observation of constant boiling behavior and constant vapor composition
• Change in color only
• Measurement of viscosity alone
• pH monitoring

Correct Answer: Observation of constant boiling behavior and constant vapor composition

Q50. How can one overcome azeotropic limitation to achieve higher purity by distillation?

• By using simple batch distillation only
• By azeotropic or extractive distillation, adding entrainers or using pressure-swing distillation
• By lowering temperature to absolute zero
• By adding inert salts that make components nonvolatile

Correct Answer: By azeotropic or extractive distillation, adding entrainers or using pressure-swing distillation

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