Factors influencing evaporation MCQs With Answer

Introduction: Understanding factors influencing evaporation MCQs with answer is essential for B. Pharm students studying drug formulation, drying, and stability. Evaporation rate depends on temperature, relative humidity, vapor pressure, surface area, air movement, solvent properties and solute concentration—critical for processes like spray-drying, granulation, and moisture control. This concise, SEO-friendly guide highlights the physical chemistry and practical pharmaceutical implications of evaporation so you can master both theory and application. Keywords covered: evaporation, factors influencing evaporation MCQs with answer, B. Pharm, vapor pressure, drying kinetics, and formulation stability. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which factor most directly increases the evaporation rate of a solvent at constant temperature?

• Decrease in surface area
• Increase in relative humidity
• Increase in air movement across the surface
• Adding a non-volatile solute

Correct Answer: Increase in air movement across the surface

Q2. According to Raoult’s law, adding a non-volatile solute to a solvent will:

• Increase the solvent’s vapor pressure
• Have no effect on vapor pressure
• Decrease the solvent’s vapor pressure
• Convert solvent to gas

Correct Answer: Decrease the solvent’s vapor pressure

Q3. Which equation relates vapor pressure and temperature for a pure substance?

• Henderson-Hasselbalch equation
• Clausius-Clapeyron equation
• Arrhenius equation
• Michaelis-Menten equation

Correct Answer: Clausius-Clapeyron equation

Q4. In pharmaceutical drying, what is the significance of the boundary layer above a liquid surface?

• It has no influence on evaporation
• It slows mass transfer, limiting evaporation rate
• It accelerates chemical reactions
• It permanently prevents vapor formation

Correct Answer: It slows mass transfer, limiting evaporation rate

Q5. How does increasing temperature affect evaporation rate assuming other factors constant?

• Evaporation rate decreases
• Evaporation rate increases
• No change in evaporation rate
• Solute concentration increases evaporation

Correct Answer: Evaporation rate increases

Q6. Which property of solvent most affects evaporation in pharmaceutical processes?

• Color of solvent
• Vapor pressure of solvent
• Electrical conductivity
• Optical rotation

Correct Answer: Vapor pressure of solvent

Q7. Relative humidity in the surrounding air influences evaporation because it changes:

• The solvent’s chemical structure
• Difference between vapor pressure and partial pressure of vapor
• Surface tension only
• Rate of solute dissolution

Correct Answer: Difference between vapor pressure and partial pressure of vapor

Q8. Which drying method is most suitable for heat-sensitive pharmaceutical powders?

• High-temperature tray drying
• Spray drying with optimized inlet temperature
• Direct flame drying
• Boiling under atmospheric pressure

Correct Answer: Spray drying with optimized inlet temperature

Q9. Evaporation is an endothermic process because it requires:

• Release of heat to surroundings
• No heat exchange
• Input of latent heat of vaporization
• Decrease in internal energy only

Correct Answer: Input of latent heat of vaporization

Q10. Which factor decreases evaporation from a liquid surface?

• Increasing air velocity
• Increasing surface area
• High ambient relative humidity
• Elevating temperature

Correct Answer: High ambient relative humidity

Q11. In the context of formulations, hygroscopic excipients affect evaporation by:

• Repelling moisture and speeding evaporation
• Attracting moisture and reducing net evaporation
• Having no interaction with water
• Converting water into non-volatile solute

Correct Answer: Attracting moisture and reducing net evaporation

Q12. The Antoine equation is used to:

• Predict solvent boiling point under pressure
• Describe adsorption isotherms
• Estimate vapor pressure as a function of temperature
• Calculate diffusion coefficients in solids

Correct Answer: Estimate vapor pressure as a function of temperature

Q13. Which parameter is most important when designing a fluidized bed dryer for granules?

• Bed color
• Air flow and temperature control
• Magnetic properties
• Electrical conductivity

Correct Answer: Air flow and temperature control

Q14. Evaporation rate is proportional to the difference between:

• Surface tension and viscosity
• Saturated vapor pressure and ambient partial pressure
• Boiling point and melting point
• pH and ionic strength

Correct Answer: Saturated vapor pressure and ambient partial pressure

Q15. In spray drying, smaller droplet size generally leads to:

• Slower drying due to reduced surface-to-volume ratio
• Faster drying due to increased surface-to-volume ratio
• No effect on drying rate
• Increased residual solvent due to coalescence

Correct Answer: Faster drying due to increased surface-to-volume ratio

Q16. Which of the following increases evaporation from a wetted tablet bed?

• Reducing air exchange in the dryer
• Increasing air humidity
• Increasing drying air temperature
• Adding non-volatile binder to the surface

Correct Answer: Increasing drying air temperature

Q17. The term “drying front” in drying kinetics refers to:

• The time when drying stops
• The region in material where moisture changes from free to bound
• The surface temperature only
• An equipment cleaning cycle

Correct Answer: The region in material where moisture changes from free to bound

Q18. Which mechanism often controls the final stage of drying for porous pharmaceutical solids?

• Convective heat transfer only
• Internal diffusion of moisture to the surface
• Immediate evaporation from bulk
• Chemical degradation of drug

Correct Answer: Internal diffusion of moisture to the surface

Q19. How does solute concentration at the evaporating surface affect evaporation?

• Higher solute concentration increases vapor pressure
• Higher solute concentration decreases vapor pressure
• Solute concentration has no effect
• Solute converts to vapor and increases evaporation

Correct Answer: Higher solute concentration decreases vapor pressure

Q20. Latent heat of vaporization influences evaporation because:

• Evaporation releases this heat to surroundings
• Evaporation requires absorption of this heat
• It decreases vapor pressure directly
• It only affects boiling, not evaporation

Correct Answer: Evaporation requires absorption of this heat

Q21. The driving force for evaporation in an open system is:

• Temperature gradient in the solid core
• Concentration gradient of vapor between surface and bulk air
• Mechanical agitation only
• Viscosity of the liquid

Correct Answer: Concentration gradient of vapor between surface and bulk air

Q22. Which measurement technique is commonly used to determine evaporation rate of a formulation sample?

• Gravimetric weight loss over time
• UV-Vis spectroscopy of solid content
• pH titration
• Electrical impedance

Correct Answer: Gravimetric weight loss over time

Q23. In closed systems, evaporation is limited by:

• Continuous removal of vapor
• Accumulation of vapor increasing ambient partial pressure
• Absence of liquid
• Temperature decrease only

Correct Answer: Accumulation of vapor increasing ambient partial pressure

Q24. Which pharmaceutical process relies heavily on controlled evaporation?

• Sterilization by autoclaving
• Spray-drying of APIs and excipients
• Centrifugation of tablets
• Lyophilization without sublimation

Correct Answer: Spray-drying of APIs and excipients

Q25. Henry’s law is most applicable to which aspect related to evaporation?

• Vapor-liquid equilibrium of non-volatile solutes
• Solubility of gases in liquids affecting headspace during drying
• Rate of solid-state diffusion during drying
• Boiling point elevation due to electrolytes

Correct Answer: Solubility of gases in liquids affecting headspace during drying

Q26. Increasing surface area of a wet film will typically:

• Decrease the evaporation rate per unit area
• Increase total evaporation due to more exposed area
• Cause immediate crystallization of solutes
• Have no effect on evaporation

Correct Answer: Increase total evaporation due to more exposed area

Q27. Which of the following reduces evaporation from a capsule surface?

• Using desiccant packaging
• Storing at low relative humidity
• Coating with moisture-barrier film
• Increasing drying temperature

Correct Answer: Coating with moisture-barrier film

Q28. The term “equilibrium moisture content” refers to:

• Moisture content at which product neither gains nor loses water
• Maximum moisture content during wetting
• Moisture content immediately after granulation
• Moisture at boiling point

Correct Answer: Moisture content at which product neither gains nor loses water

Q29. During drying, the constant-rate period is characterized by:

• Surface moisture removal controlled by external conditions
• Internal diffusion control with slow rate
• Complete loss of all free water
• Immediate chemical degradation

Correct Answer: Surface moisture removal controlled by external conditions

Q30. For a volatile solvent with high vapor pressure, which is true?

• It evaporates more slowly at a given temperature
• It evaporates more rapidly at a given temperature
• Vapor pressure does not affect evaporation speed
• It always causes product to become hygroscopic

Correct Answer: It evaporates more rapidly at a given temperature

Q31. Which equipment parameter most influences evaporation uniformity in a tray dryer?

• Tray color
• Airflow distribution and temperature uniformity
• Tray material magnetic properties
• Electrical power factor

Correct Answer: Airflow distribution and temperature uniformity

Q32. The presence of volatile impurities in a solvent will:

• Not affect evaporation behavior
• Potentially change vapor composition and evaporation rate
• Always reduce overall evaporation rate
• Convert solvent to a non-volatile phase

Correct Answer: Potentially change vapor composition and evaporation rate

Q33. Which property of air most strongly affects convective evaporation?

• Air taste
• Air velocity and humidity
• Air color
• Air electrical charge only

Correct Answer: Air velocity and humidity

Q34. In drying kinetics, Fick’s law primarily describes:

• Convective heat transfer
• Diffusive mass transfer of moisture within solids
• Chemical reaction rates during drying
• Light absorption by wet films

Correct Answer: Diffusive mass transfer of moisture within solids

Q35. Why is controlling moisture content important for pharmaceutical stability?

• Moisture has no effect on chemical stability
• Excess moisture can promote hydrolysis, microbial growth, and physical changes
• High moisture always improves shelf life
• Only aesthetics are affected by moisture

Correct Answer: Excess moisture can promote hydrolysis, microbial growth, and physical changes

Q36. Which is a sign that a drying process has reached the falling-rate period?

• Surface remains saturated with free water
• Drying rate becomes dependent on internal moisture diffusion
• Evaporation becomes infinitely fast
• Moisture content increases unexpectedly

Correct Answer: Drying rate becomes dependent on internal moisture diffusion

Q37. Using vacuum during evaporation typically:

• Raises the boiling point of the solvent
• Lowers the boiling point and can speed evaporation at lower temperatures
• Has no effect on evaporation conditions
• Prevents vapor formation completely

Correct Answer: Lowers the boiling point and can speed evaporation at lower temperatures

Q38. Which factor increases the saturated vapor pressure of a liquid?

• Decreasing temperature
• Increasing temperature
• Adding a non-volatile solute
• Decreasing surface area

Correct Answer: Increasing temperature

Q39. Residual solvent limits in final pharmaceutical products relate to evaporation because:

• Evaporation always removes all solvent
• Incomplete evaporation can leave harmful residual solvents impacting safety
• Residual solvents improve tablet hardness
• Residual solvent levels are unrelated to drying

Correct Answer: Incomplete evaporation can leave harmful residual solvents impacting safety

Q40. Which effect does air recirculation without dehumidification have on evaporation?

• Promotes continuous high evaporation
• Reduces evaporation as ambient humidity builds up
• Eliminates need for heating
• Causes immediate crystallization of solvent

Correct Answer: Reduces evaporation as ambient humidity builds up

Q41. In formulations, evaporation-induced supersaturation can lead to:

• Precipitation or crystallization of the drug
• Permanent solubilization
• Decrease in solute concentration
• No physical changes

Correct Answer: Precipitation or crystallization of the drug

Q42. Which approach helps maintain evaporation while protecting heat-sensitive APIs?

• Increase temperature to maximum
• Use reduced pressure and moderate temperatures
• Prolong exposure to direct sunlight
• Avoid using any dryers

Correct Answer: Use reduced pressure and moderate temperatures

Q43. The mass transfer coefficient in convective evaporation is influenced by:

• Air flow regime and properties of the air-liquid interface
• Only the chemical identity of solutes
• The color of the drying chamber
• The taste of the solvent

Correct Answer: Air flow regime and properties of the air-liquid interface

Q44. Which solvent characteristic generally leads to faster evaporation at room temperature?

• High boiling point
• Low vapor pressure
• High vapor pressure and low boiling point
• High viscosity only

Correct Answer: High vapor pressure and low boiling point

Q45. Drying a film-coated tablet too quickly may cause:

• Improved mechanical strength always
• Coating defects like cracking or peeling
• Reduced dissolution variability only
• No impact on product quality

Correct Answer: Coating defects like cracking or peeling

Q46. The rate-limiting step for evaporation from a porous matrix is often:

• Surface evaporation only
• Internal moisture diffusion to surface
• External convective heat exchange only
• Photolytic degradation

Correct Answer: Internal moisture diffusion to surface

Q47. Which of the following reduces evaporation losses during open handling of solvents?

• Increase uncovered surface area
• Cover containers and use fume hoods
• Raise ambient temperature significantly
• Stir vigorously in open air

Correct Answer: Cover containers and use fume hoods

Q48. In drying curves, a plateau in temperature during constant-rate drying indicates:

• Surface temperature remains near wet-bulb temperature due to evaporation
• Drying has finished
• Product temperature is uncontrolled and rising
• Equipment failure

Correct Answer: Surface temperature remains near wet-bulb temperature due to evaporation

Q49. Why is control of solvent evaporation important during coating operations?

• It prevents uniform film formation and ensures defects
• It ensures solvent remains indefinitely in the film
• It controls film drying rate to achieve uniform coating and avoid defects
• It is irrelevant to coating integrity

Correct Answer: It controls film drying rate to achieve uniform coating and avoid defects

Q50. When designing a drying process, which combination is typically optimized to achieve efficient evaporation without degrading API?

• High temperature, high humidity, no airflow
• Moderate temperature, controlled low humidity, adequate airflow
• Low temperature, high humidity, stagnant air
• No temperature control, random humidity

Correct Answer: Moderate temperature, controlled low humidity, adequate airflow

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