Changes in states of matter MCQs With Answer

Introduction: Changes in states of matter MCQs With Answer are essential for B. Pharm students studying phase transitions, solid-state chemistry, and physical pharmacy. This focused set covers melting point, boiling point, sublimation, vapor pressure, enthalpy of fusion, polymorphism, crystallinity, amorphous forms, phase diagrams, and analytical methods like DSC and TGA. Understanding these concepts is crucial for drug stability, solubility, dissolution rates, and formulation design. The questions emphasize applied scenarios in pharmaceuticals, linking thermodynamics to practical issues such as hygroscopicity, storage conditions, and processing. Clear explanations and targeted practice will strengthen exam readiness and professional competence. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the term for the temperature at which a solid and its liquid are in equilibrium at a given pressure?

• Boiling point
• Triple point
• Melting point
• Glass transition temperature

Correct Answer: Melting point

Q2. Which process describes the transition from solid directly to gas without passing through the liquid phase?

• Condensation
• Sublimation
• Deposition
• Vaporization

Correct Answer: Sublimation

Q3. In a phase diagram, the triple point represents:

• The condition where solid and gas coexist only
• The condition where solid, liquid, and gas coexist in equilibrium
• The critical temperature above which gas cannot be liquefied
• The temperature at which a liquid boils at 1 atm

Correct Answer: The condition where solid, liquid, and gas coexist in equilibrium

Q4. Which thermal analysis technique measures heat flow associated with phase transitions like melting?

• TGA (Thermogravimetric Analysis)
• DSC (Differential Scanning Calorimetry)
• IR Spectroscopy
• X-ray Diffraction

Correct Answer: DSC (Differential Scanning Calorimetry)

Q5. The energy required to convert 1 mole of a solid into the liquid at its melting point is called:

• Specific heat capacity
• Enthalpy of vaporization
• Enthalpy of fusion
• Free energy of formation

Correct Answer: Enthalpy of fusion

Q6. Which state of matter is characterized by long-range order and a defined lattice structure?

• Amorphous solid
• Liquid crystal
• Crystalline solid
• Supercritical fluid

Correct Answer: Crystalline solid

Q7. Polymorphism in pharmaceuticals refers to:

• The ability of a compound to form salts
• The presence of impurities in a drug substance
• The occurrence of different crystalline forms of the same compound
• Conversion of liquid to gas at different pressures

Correct Answer: The occurrence of different crystalline forms of the same compound

Q8. Which term describes a solid without long-range crystalline order?

• Polymorph
• Amorphous
• Crystalline
• Isomorphous

Correct Answer: Amorphous

Q9. Vapor pressure of a liquid increases when:

• Temperature decreases
• Surface area decreases
• Temperature increases
• Boiling point increases

Correct Answer: Temperature increases

Q10. The critical point on a phase diagram indicates:

• The coexistence of all three phases
• The highest temperature and pressure at which liquid and gas are distinct
• The melting point at standard pressure
• The temperature where solid sublimates at 1 atm

Correct Answer: The highest temperature and pressure at which liquid and gas are distinct

Q11. Which process is endothermic and requires absorption of heat to occur?

• Freezing
• Condensation
• Melting
• Deposition

Correct Answer: Melting

Q12. In solid-state pharmaceuticals, hygroscopicity refers to:

• Propensity to sublime under vacuum
• Ability to absorb moisture from the environment
• Rate of crystallization during cooling
• Solubility in organic solvents

Correct Answer: Ability to absorb moisture from the environment

Q13. Which analytical method is best suited to study weight loss due to decomposition or solvent loss on heating?

• DSC
• TGA
• NMR
• UV-Vis Spectroscopy

Correct Answer: TGA

Q14. Glass transition temperature (Tg) is most relevant for which type of solid?

• Crystalline salt
• Amorphous polymer or glassy material
• Metallic crystal
• Covalent network solid like diamond

Correct Answer: Amorphous polymer or glassy material

Q15. Which factor most directly affects the melting point of a crystalline drug?

• Particle size only
• Extent of hydrogen bonding and lattice energy
• Color of the compound
• Exposure to light

Correct Answer: Extent of hydrogen bonding and lattice energy

Q16. Which of the following is a consequence of polymorphism for pharmaceuticals?

• Identical dissolution rates for all forms
• Different melting points and solubilities among forms
• Always lower bioavailability
• Polymorphs are chemically different compounds

Correct Answer: Different melting points and solubilities among forms

Q17. Which term describes the pressure of a vapor in equilibrium with its liquid at a given temperature?

• Osmotic pressure
• Vapor pressure
• Partial pressure of inert gas
• Vaporization constant

Correct Answer: Vapor pressure

Q18. A supercritical fluid exhibits properties of both gas and liquid above its:

• Triple point
• Melting point
• Critical temperature and pressure
• Glass transition temperature

Correct Answer: Critical temperature and pressure

Q19. Which statement about latent heat is correct?

• It is the heat required to raise temperature by 1°C
• It is energy absorbed or released during a phase change without temperature change
• It applies only to vaporization, not fusion
• It increases the molar mass of a substance

Correct Answer: It is energy absorbed or released during a phase change without temperature change

Q20. Which measurement is commonly used to detect polymorphic transitions in a drug substance?

• Optical rotation
• Differential Scanning Calorimetry (DSC)
• pH titration
• Flame test

Correct Answer: Differential Scanning Calorimetry (DSC)

Q21. Deposition is the phase change from:

• Liquid to gas
• Gas to solid
• Solid to liquid
• Liquid to solid

Correct Answer: Gas to solid

Q22. How does crystallinity influence dissolution rate of a drug?

• Higher crystallinity usually increases dissolution rate
• Amorphous form often dissolves faster than the crystalline form
• Crystallinity has no effect on dissolution
• Only particle color affects dissolution

Correct Answer: Amorphous form often dissolves faster than the crystalline form

Q23. Which of the following best describes a eutectic mixture?

• A single-component crystalline solid
• A mixture that melts at a single, lower temperature than either component
• A liquid solution that does not crystallize
• A gas-solid equilibrium point

Correct Answer: A mixture that melts at a single, lower temperature than either component

Q24. In a closed system at equilibrium, which of the following applies to vapor and liquid?

• Vapor pressure remains constant at a given temperature
• Vapor pressure continuously increases over time
• Vapor pressure equals atmospheric pressure only
• Liquid pressure is always zero

Correct Answer: Vapor pressure remains constant at a given temperature

Q25. Which technique can determine crystal structure and degree of crystallinity?

• Mass spectrometry
• X-ray Powder Diffraction (XRPD)
• Polarimetry
• Thin layer chromatography

Correct Answer: X-ray Powder Diffraction (XRPD)

Q26. Which statement about boiling point is true?

• Boiling point decreases with increased external pressure
• Boiling point is independent of intermolecular forces
• Boiling point is the temperature where vapor pressure equals external pressure
• Boiling point is the same as melting point

Correct Answer: Boiling point is the temperature where vapor pressure equals external pressure

Q27. Which property is most likely to change when a crystalline drug converts to an amorphous form?

• Molecular formula
• Intrinsic solubility
• Number of atoms
• Optical isomerism

Correct Answer: Intrinsic solubility

Q28. Which phase change is responsible for frost formation on a cold surface?

• Evaporation
• Sublimation
• Deposition
• Melting

Correct Answer: Deposition

Q29. Which factor does not directly affect vapor pressure of a pure liquid?

• Temperature
• Intermolecular forces
• Presence of non-volatile solute in the liquid
• Color of the liquid

Correct Answer: Color of the liquid

Q30. Solvate formation (e.g., hydrates) involves:

• Incorporation of solvent molecules into the crystal lattice
• Covalent bonding between solvent and solute only at pH extremes
• Complete loss of crystallinity
• Formation of gaseous products

Correct Answer: Incorporation of solvent molecules into the crystal lattice

Q31. Which term describes the heat released when a gas condenses to liquid?

• Heat of fusion
• Specific heat
• Enthalpy of vaporization (released)
• Calorimetric constant

Correct Answer: Enthalpy of vaporization (released)

Q32. A drug stored above its glass transition temperature (Tg) is likely to:

• Remain rigid and stable
• Have increased molecular mobility and possible physical instability
• Undergo immediate chemical decomposition only
• Crystallize into a metallic solid

Correct Answer: Have increased molecular mobility and possible physical instability

Q33. Which is a common consequence of high humidity on anhydrous drug crystals?

• Increased vaporization
• Formation of hydrates or deliquescence
• Immediate melting at room temperature
• Conversion to supercritical fluid

Correct Answer: Formation of hydrates or deliquescence

Q34. The Clapeyron equation relates which two properties across a phase boundary?

• Viscosity and density
• Pressure and temperature changes to enthalpy and volume change
• Molar mass and refractive index
• Solubility and pH

Correct Answer: Pressure and temperature changes to enthalpy and volume change

Q35. Why is polymorph screening important in drug development?

• Polymorphs are irrelevant to patenting
• Different polymorphs can affect bioavailability, stability, and manufacturability
• Polymorphs always have identical shelf life
• Screening reduces the need for dissolution testing

Correct Answer: Different polymorphs can affect bioavailability, stability, and manufacturability

Q36. Which phenomenon describes a solid absorbing enough moisture to dissolve into its own absorbed water?

• Hygroscopy
• Deliquescence
• Efflorescence
• Osmosis

Correct Answer: Deliquescence

Q37. Which of the following is true for supercooled liquids?

• They crystallize quickly at any temperature above 0 K
• They remain liquid below their normal freezing point without crystallizing
• They are another term for polymers above Tg
• They are always gaseous

Correct Answer: They remain liquid below their normal freezing point without crystallizing

Q38. Which physical pharmacy parameter is influenced by surface area resulting from solid-state changes?

• Melting point only
• Dissolution rate
• Molar mass
• Boiling point at 1 atm

Correct Answer: Dissolution rate

Q39. Which solid form is generally least stable thermodynamically at ambient conditions?

• Thermodynamic stable polymorph
• Amorphous form
• Hydrate form
• Most dense crystal form

Correct Answer: Amorphous form

Q40. The process of desiccation in pharmaceuticals aims to:

• Increase moisture content
• Remove moisture to improve stability
• Convert crystalline to amorphous form intentionally
• Enhance solubility by adding water

Correct Answer: Remove moisture to improve stability

Q41. Which factor can cause a shift in melting point observed by DSC?

• Sample purity
• Ambient light intensity
• Magnetic field around the instrument
• Color of DSC pan

Correct Answer: Sample purity

Q42. In the context of phase equilibrium, Raoult’s law applies to:

• Ideal solutions relating partial vapor pressures to mole fractions
• Non-volatile solutes only
• Pure solids at their melting point
• Gases under extremely high pressure only

Correct Answer: Ideal solutions relating partial vapor pressures to mole fractions

Q43. Which process is used to determine loss of volatile content (e.g., water) from a drug by heating?

• X-ray diffraction
• Thermogravimetric analysis (TGA)
• High-performance liquid chromatography
• Optical microscopy

Correct Answer: Thermogravimetric analysis (TGA)

Q44. Which description best fits adsorption as opposed to absorption?

• Molecules penetrate the bulk of a material
• Molecules accumulate at the surface of a solid or liquid
• Complete mixing in solution
• Conversion of gas to liquid only

Correct Answer: Molecules accumulate at the surface of a solid or liquid

Q45. Why might a metastable polymorph be preferred in formulation?

• It is always cheaper to produce
• It may have higher solubility and faster dissolution improving bioavailability
• Metastable forms never convert to stable forms
• Regulatory guidance prohibits use of stable forms

Correct Answer: It may have higher solubility and faster dissolution improving bioavailability

Q46. Which factor typically lowers the boiling point of a liquid?

• Increasing external pressure
• Presence of a non-volatile solute
• Decreasing external pressure
• Stronger intermolecular attractions

Correct Answer: Decreasing external pressure

Q47. In pharmaceutical solids, efflorescence refers to:

• Absorption of water to form a hydrate
• Loss of water from a hydrate resulting in powdery surface crystals
• Complete dissolution on exposure to humidity
• Conversion to supercritical fluid at room temperature

Correct Answer: Loss of water from a hydrate resulting in powdery surface crystals

Q48. Which of these is NOT typically influenced by a drug’s solid-state form?

• Melting point
• Mechanical properties affecting tableting
• Molecular weight of the drug molecule
• Dissolution behavior

Correct Answer: Molecular weight of the drug molecule

Q49. Clausius–Clapeyron equation is most useful for:

• Predicting change in vapor pressure with temperature
• Calculating glass transition temperatures
• Measuring particle size distribution
• Determining crystal habit by microscopy

Correct Answer: Predicting change in vapor pressure with temperature

Q50. Which practice helps to maintain stability of hygroscopic drug powders during storage?

• Storing at high relative humidity
• Packaging with desiccants and moisture-barrier containers
• Keeping samples above their Tg
• Exposing to sunlight to dry them

Correct Answer: Packaging with desiccants and moisture-barrier containers

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