Displacement value and its calculation MCQs With Answer

Introduction: Displacement value is a key pharmaceutical calculation used in suppository and some dosage-form formulations to predict how much base (or vehicle) is displaced when an active drug is incorporated. B. Pharm students must master the concept, its relation to density and specific gravity, and the standard formulas for practical batch and per-unit calculations. This topic covers definition, conversion between reciprocal definitions, calculation from densities (D = density of base / density of drug), and application to per‑suppository and batch preparations. Clear understanding prevents dosing errors and ensures correct product weight and consistency. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the standard pharmaceutical definition of displacement value in suppository formulation?

• The weight of drug that will displace 1 g of suppository base
• The weight of base displaced by 1 g of drug
• The volume of base displaced by 1 g of drug
• The ratio of drug to base by volume

Correct Answer: The weight of base displaced by 1 g of drug

Q2. Which formula correctly gives the amount of suppository base (per unit) required when displacement value (D) is known?

• Base required = Total mould weight + (D × weight of drug)
• Base required = Total mould weight – (D × weight of drug)
• Base required = Total mould weight ÷ (D × weight of drug)
• Base required = (Weight of drug ÷ D) – Total mould weight

Correct Answer: Base required = Total mould weight – (D × weight of drug)

Q3. If the density of base = 0.9 g/mL and density of drug = 1.8 g/mL, what is the displacement value D (base displaced by 1 g drug)?

• 0.50
• 2.00
• 1.20
• 0.20

Correct Answer: 0.50

Q4. A mould holds 2.00 g of pure base. For each suppository you add 0.20 g drug; displacement value D = 0.50. How much base is required per suppository?

• 1.90 g
• 1.80 g
• 1.60 g
• 2.10 g

Correct Answer: 1.90 g

Q5. If one definition of displacement value is “weight of base displaced by 1 g of drug” (D), what is the reciprocal definition often used in some texts?

• Weight of drug displaced by 1 g base (1/D)
• Volume of drug displaced by 1 g base
• Density of drug minus density of base
• Specific gravity of base divided by drug

Correct Answer: Weight of drug displaced by 1 g base (1/D)

Q6. How is displacement value (D) related to densities (or specific gravities) of base (ρb) and drug (ρa)?

• D = ρa / ρb
• D = ρb × ρa
• D = ρb / ρa
• D = 1 / (ρb × ρa)

Correct Answer: D = ρb / ρa

Q7. If specific gravity of base = 0.9 and specific gravity of drug = 1.2, what is D?

• 1.33
• 0.75
• 0.90
• 1.20

Correct Answer: 0.75

Q8. For a 2.0 g mould, drug per suppository = 0.50 g, displacement value D = 0.25. Base needed per suppository is:

• 1.875 g
• 1.25 g
• 1.00 g
• 1.50 g

Correct Answer: 1.875 g

Q9. If D < 1, what does this imply about relative densities of base and drug?

• Base is denser than drug
• Drug is denser than base
• Both have equal densities
• Density cannot be inferred

Correct Answer: Drug is denser than base

Q10. You plan 50 suppositories; each mould nominal capacity (pure base) = 2.00 g. Each contains 0.10 g drug; D=0.50. What is the total base required for the batch?

• 97.50 g
• 100.00 g
• 95.00 g
• 90.00 g

Correct Answer: 97.50 g

Q11. Holding drug weight constant, increasing displacement value D will have what effect on base required per unit (using base = W – D×Wa)?

• Base required increases
• Base required decreases
• No effect on base required
• Base required becomes equal to drug weight

Correct Answer: Base required decreases

Q12. If density of base = density of drug, what is the displacement value D and practical implication?

• D = 0; displacement irrelevant
• D = 1; drug displaces base equally by weight
• D > 1; base much denser
• D < 1; drug much denser

Correct Answer: D = 1; drug displaces base equally by weight

Q13. Which calculation gives the number of suppositories from a batch when you know total mass of base available and base required per unit?

• Number = Total base ÷ (Total base – D×Wa)
• Number = Total base × (D × Wa)
• Number = Total base ÷ Base required per suppository
• Number = (Total base + Wa) ÷ D

Correct Answer: Number = Total base ÷ Base required per suppository

Q14. A drug has specific gravity 2.0; base SG = 0.8. Displacement value D = ?

• 2.50
• 0.40
• 1.60
• 0.25

Correct Answer: 0.40

Q15. Suppose D is defined in your reference as “weight of drug that displaces 1 g of base” and equals 0.5. What is the equivalent D (base displaced per 1 g drug) used in the formula base = W – D×Wa?

• 2.0
• 0.5
• 1.5
• 0.25

Correct Answer: 2.0

Q16. You must prepare 30 suppositories, each mould nominal capacity (pure base) 2.5 g. Each contains 0.25 g drug; D = 0.8. What is total base required? (Per-unit base = 2.5 – 0.8×0.25)

• 72.00 g
• 71.00 g
• 69.00 g
• 75.00 g

Correct Answer: 72.00 g

Q17. True or false: Displacement value is irrelevant for very low-dose drugs in suppository preparation.

• True — always negligible for low doses
• False — it can still affect weight and uniformity
• True — only density matters
• False — but only for oral tablets

Correct Answer: False — it can still affect weight and uniformity

Q18. For a liquid drug with same density as the base, displacement value will be approximately:

• 0 (zero)
• 1 (unity)
• > 1 (greater than one)
• < 0 (negative)

Correct Answer: 1 (unity)

Q19. If you ignore displacement value in calculations, common consequence is:

• Improved dissolution of drug
• Incorrect dose per unit and inconsistent weights
• Higher melting point of base
• No effect on product quality

Correct Answer: Incorrect dose per unit and inconsistent weights

Q20. Which property is directly used to calculate displacement value from physical data?

• Melting point
• Viscosity
• Density or specific gravity
• Surface tension

Correct Answer: Density or specific gravity

Q21. A drug of density 1.5 g/mL is added to a base of density 0.75 g/mL. What is the displacement value D (base displaced per 1 g drug)?

• 0.50
• 2.00
• 1.00
• 0.25

Correct Answer: 0.50

Q22. If per-suppository drug weight is Wa and you calculate base as W – D×Wa, which quantity W represents?

• The weight of drug-free base that fills the mould (mould capacity expressed as weight)
• The weight of active drug per batch
• The melting point of base in degrees
• The volume of drug in mL

Correct Answer: The weight of drug-free base that fills the mould (mould capacity expressed as weight)

Q23. For batch scaling: if per-unit base required = 1.84 g and you need 100 units, which of the following gives total base required?

• 1.84 g
• 184 g
• 18.4 g
• 1840 g

Correct Answer: 184 g

Q24. Which scenario most strongly requires using displacement value in formulation?

• When drug amount is negligible <0.001% w/w
• When drug amount is substantial and densities differ from base
• When working with gases
• When measuring pH only

Correct Answer: When drug amount is substantial and densities differ from base

Q25. A base has SG 0.95, drug SG 1.90. What is D and what does that numerically indicate?

• D = 2.00; 1 g drug displaces 2 g base
• D = 0.50; 1 g drug displaces 0.50 g base
• D = 1.00; densities equal
• D = 0.25; 1 g drug displaces 0.25 g base

Correct Answer: D = 0.50; 1 g drug displaces 0.50 g base

Q26. If displacement value (base displaced per 1 g drug) is 0.6 and per-unit drug weight = 0.3 g, how much base is displaced by the drug per unit?

• 0.18 g
• 0.50 g
• 0.30 g
• 0.60 g

Correct Answer: 0.18 g

Q27. A textbook gives displacement value as “weight of medicament which displaces 1 g of base.” If medicament weight that displaces 1 g base = 0.4 g, which formula should you use to compute base required (W mould weight, Wa drug)?

• Base = W – (Wa × 0.4)
• Base = W – (Wa ÷ 0.4)
• Base = W + (Wa ÷ 0.4)
• Base = Wa ÷ W

Correct Answer: Base = W – (Wa ÷ 0.4)

Q28. For a mould of capacity 3.0 g, drug per unit 0.6 g, and D (base displaced per 1 g drug) = 0.2, base required per unit is:

• 2.88 g
• 2.88 g (calculated as 3.0 – 0.2×0.6)
• 2.00 g
• 3.12 g

Correct Answer: 2.88 g (calculated as 3.0 – 0.2×0.6)

Q29. Which practical laboratory measurement can be used to determine displacement value experimentally?

• Measure melting point of drug in base
• Measure mass of mould filled with pure base and then with known drug amount and calculate displaced base
• Measure refractive index only
• Measure color change on mixing

Correct Answer: Measure mass of mould filled with pure base and then with known drug amount and calculate displaced base

Q30. Why is displacement value important beyond suppositories (general formulation impact)?

• It helps predict volume changes and dosing in any formulation where a solid or liquid active replaces vehicle by volume
• It determines chemical stability of drug
• It only affects flavoring agents
• It replaces the need for dissolution testing

Correct Answer: It helps predict volume changes and dosing in any formulation where a solid or liquid active replaces vehicle by volume

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