Efflorescent and hygroscopic powders MCQs With Answer

Efflorescent and hygroscopic powders are vital topics for B. Pharm students studying formulation and stability. Efflorescent powders lose water of crystallization and may crumble, while hygroscopic powders absorb moisture, becoming sticky or even deliquescent. Key concepts include moisture sorption, equilibrium relative humidity (ERH), critical relative humidity (CRH/DRH), water of hydration, and measurement methods such as dynamic vapor sorption and Karl Fischer titration. These properties influence flow, compressibility, dissolution, chemical stability, and packaging decisions. Understanding examples, control strategies (desiccants, coatings, moisture‑proof packaging), and monitoring techniques is essential for robust drug product design. Mastering these concepts aids optimal powder handling, storage conditions, and moisture content monitoring in pharmaceutical manufacturing. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What defines an efflorescent powder?

• A substance that absorbs moisture and liquefies
• A substance that melts at low temperature
• A substance that loses water of crystallization when exposed to air
• A substance that sublimes on drying

Correct Answer: A substance that loses water of crystallization when exposed to air

Q2. Which statement best describes a hygroscopic powder?

• A powder that releases water and becomes brittle
• A powder that absorbs moisture from the atmosphere
• A powder that undergoes polymorphic transition on heating
• A powder that resists moisture uptake

Correct Answer: A powder that absorbs moisture from the atmosphere

Q3. What is deliquescence?

• The process where a solid releases bound water to form a hydrate
• The process where a solid absorbs moisture to the extent of dissolving and forming a solution
• The formation of a stable crystalline hydrate
• The irreversible oxidation of a hygroscopic powder

Correct Answer: The process where a solid absorbs moisture to the extent of dissolving and forming a solution

Q4. Which of the following is a common example of an efflorescent substance?

• Sodium carbonate decahydrate (washing soda)
• Calcium chloride
• Polyethylene glycol
• Sucrose

Correct Answer: Sodium carbonate decahydrate (washing soda)

Q5. Which salt is typically strongly hygroscopic and often deliquescent?

• Sodium sulfate
• Potassium nitrate
• Calcium chloride
• Sodium chloride

Correct Answer: Calcium chloride

Q6. Mechanistically, why does an efflorescent hydrate lose water?

• Because its vapour pressure of water is lower than ambient
• Because the vapour pressure of bound water in the hydrate is higher than the surrounding air
• Because it reacts chemically with oxygen
• Because it sublimes at room temperature

Correct Answer: Because the vapour pressure of bound water in the hydrate is higher than the surrounding air

Q7. Which instrument is commonly used for precise moisture sorption isotherm measurement?

• Differential scanning calorimeter (DSC)
• Dynamic vapor sorption (DVS) analyzer
• High-performance liquid chromatograph (HPLC)
• Thermogravimetric analyzer (TGA) only

Correct Answer: Dynamic vapor sorption (DVS) analyzer

Q8. What does CRH (critical relative humidity) refer to?

• The RH at which a solid begins to melt
• The RH below which a substance is always deliquescent
• The RH at which a dry powder begins to take up moisture rapidly
• The RH at which water boils at room temperature

Correct Answer: The RH at which a dry powder begins to take up moisture rapidly

Q9. Equilibrium relative humidity (ERH) for a hydrate indicates:

• The RH at which the hydrate and its anhydrous form are in equilibrium with ambient moisture
• The RH at which the substance sublimes
• The RH at which the powder becomes flammable
• The RH at which the powder loses all moisture

Correct Answer: The RH at which the hydrate and its anhydrous form are in equilibrium with ambient moisture

Q10. How does hygroscopicity commonly affect tablet properties?

• Improves hardness and stability
• Causes increased flowability and reduced stickiness
• Leads to caking, loss of flowability, and decreased hardness
• Has no effect on dissolution rate

Correct Answer: Leads to caking, loss of flowability, and decreased hardness

Q11. Which analytical method is most specific for determining water content (including water of hydration)?

• Loss on drying (LOD) gravimetric method
• Karl Fischer titration
• UV–Vis spectrophotometry
• HPLC with refractive index detection

Correct Answer: Karl Fischer titration

Q12. Which excipient is known to increase the hygroscopicity of a formulation?

• Magnesium stearate
• Microcrystalline cellulose (MCC)
• Polyethylene glycol (PEG)
• Calcium phosphate

Correct Answer: Polyethylene glycol (PEG)

Q13. Which control strategy is most appropriate to protect hygroscopic powders during storage?

• Storage in open trays at room humidity
• Use of moisture‑proof primary packaging and desiccants
• Exposure to high humidity to equilibrate
• Storage at elevated temperature only

Correct Answer: Use of moisture‑proof primary packaging and desiccants

Q14. What parameter specifically predicts whether a salt will deliquesce at a given RH?

• Deliquescence relative humidity (DRH)
• Melting point
• pKa
• Particle size distribution

Correct Answer: Deliquescence relative humidity (DRH)

Q15. Moisture uptake can lower which thermal property of an amorphous powder, causing stickiness?

• Melting point
• Glass transition temperature (Tg)
• Boiling point
• Cp (heat capacity) only

Correct Answer: Glass transition temperature (Tg)

Q16. What typically happens to an efflorescent hydrate on prolonged exposure to dry air?

• It gains water and becomes deliquescent
• It loses water, decreases in mass, and may form an anhydrous solid
• It polymerizes to a higher molecular weight
• It becomes more crystalline and increases in size

Correct Answer: It loses water, decreases in mass, and may form an anhydrous solid

Q17. Which packaging approach is best for very hygroscopic pharmaceutical powders?

• Permeable paper bags
• Moisture‑proof (airtight) containers with desiccant sachets
• Open drums stored in a humid room
• Cardboard boxes without inner lining

Correct Answer: Moisture‑proof (airtight) containers with desiccant sachets

Q18. Compared with crystalline materials, amorphous powders generally:

• Show lower moisture uptake at all relative humidities
• Show higher and more variable moisture uptake and greater sensitivity to humidity
• Are always non‑hygroscopic
• Do not exhibit glass transition

Correct Answer: Show higher and more variable moisture uptake and greater sensitivity to humidity

Q19. Which technique is used to estimate surface area relevant to moisture adsorption?

• BET nitrogen adsorption
• IR spectroscopy
• Polarimetry
• Atomic absorption spectroscopy

Correct Answer: BET nitrogen adsorption

Q20. How can efflorescence change the apparent assay (percent w/w) of an API in a powder?

• By increasing the actual amount of API through chemical reaction
• By losing water mass, which can increase percent w/w of the remaining dry API
• By causing the API to become volatile and escape
• By changing the pH of the powder

Correct Answer: By losing water mass, which can increase percent w/w of the remaining dry API

Q21. During wet granulation of a hygroscopic drug, which practice reduces moisture‑related problems?

• Operate in high humidity and avoid drying steps
• Control environmental humidity and apply adequate drying or use dry granulation/coating
• Increase binder concentration indefinitely
• Exclude milling steps

Correct Answer: Control environmental humidity and apply adequate drying or use dry granulation/coating

Q22. Which common pharmaceutical sugar is notably hygroscopic?

• Lactose monohydrate (always non‑hygroscopic)
• Sucrose
• Mannitol (highly deliquescent)
• Starch (completely hydrophobic)

Correct Answer: Sucrose

Q23. A deliquescent salt will begin to form a solution when ambient RH:

• Is lower than its DRH
• Exceeds its deliquescence relative humidity (DRH)
• Is at 0% RH
• Remains constant at all temperatures

Correct Answer: Exceeds its deliquescence relative humidity (DRH)

Q24. Which laboratory method is suitable for generating a moisture sorption isotherm?

• Gravimetric moisture sorption at controlled RH points
• Simple light microscopy
• pH titration
• Thin‑layer chromatography

Correct Answer: Gravimetric moisture sorption at controlled RH points

Q25. Hygroscopicity most directly compromises which powder attribute during handling?

• Taste only
• Flowability, often causing caking and poor dosing uniformity
• Color intensity exclusively
• Optical rotation

Correct Answer: Flowability, often causing caking and poor dosing uniformity

Q26. A simple experimental indicator of efflorescence in a sample is:

• Increase in sample melting point
• Visual appearance of a crystalline powder after loss of bound water and measurable weight loss
• Complete dissolution in nonpolar solvents
• Change in UV absorbance at 800 nm

Correct Answer: Visual appearance of a crystalline powder after loss of bound water and measurable weight loss

Q27. Which of the following is least hygroscopic and often used as a moisture‑sensitive lubricant?

• Polyethylene glycol (PEG)
• Magnesium stearate
• Glycerol
• Sorbitol

Correct Answer: Magnesium stearate

Q28. The term that best describes binding of water molecules to the surface of a solid is:

• Absorption
• Adsorption
• Osmosis
• Ionization

Correct Answer: Adsorption

Q29. A primary formulation risk posed by deliquescent contaminants is:

• Reduced molecular weight of the API
• Liquefaction of powder bulk leading to dosing errors and stability loss
• Improved flow and compressibility
• Permanent inertization of excipients

Correct Answer: Liquefaction of powder bulk leading to dosing errors and stability loss

Q30. Which operational measure reduces the risk of efflorescence and hygroscopic damage during storage?

• Store above the CRH/DRH to equilibrate rapidly
• Maintain storage RH below critical limits and use moisture‑proof packaging with desiccants
• Store powders in open air to allow natural equilibration
• Only increase storage temperature without controlling RH

Correct Answer: Maintain storage RH below critical limits and use moisture‑proof packaging with desiccants

Download