Pharmaceutical calculations using alligation method MCQs With Answer

Pharmaceutical calculations using alligation method MCQs With Answer

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Pharmaceutical calculations using the alligation method are essential for B. Pharm students to master accurate mixture and concentration problems in compounding, formulation, and quality control. This introduction explains practical use of the alligation rule to determine proportions of different strengths, compute final concentration after mixing, handle dilutions, unit conversions, and potency adjustments. Emphasizing stepwise reasoning and typical pharmacy scenarios—percent w/v, mg/mL, and ratio problems—builds confidence for lab work and exams. These focused MCQs challenge conceptual understanding and calculation speed while reinforcing error-checking strategies and common pitfalls in mixture problems. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary purpose of the alligation method in pharmaceutical calculations?

  • To determine the mixing ratio of solutions with different strengths to obtain a desired strength
  • To calculate drug stability under different temperatures
  • To convert units between molarity and normality
  • To determine the pH of buffer solutions

Correct Answer: To determine the mixing ratio of solutions with different strengths to obtain a desired strength

Q2. Using alligation, what is the ratio of 10% solution to 30% solution to obtain 18% solution?

  • 2:3
  • 3:2
  • 1:2
  • 2:1

Correct Answer: 3:2

Q3. To prepare 20 L of 15% solution using 10% and 25% solutions, how many liters of 10% solution are required?

  • 10 L
  • 6.67 L
  • 13.33 L
  • 15 L

Correct Answer: 13.33 L

Q4. In alligation, the term “medial” refers to which value?

  • The average or desired concentration between two strengths
  • The stronger concentration among the two
  • The volume of solvent to remove
  • The dilution factor only for aqueous solutions

Correct Answer: The average or desired concentration between two strengths

Q5. If you mix 200 mL of 8% solution with 300 mL of 12% solution, what is the final concentration?

  • 10.4%
  • 9.6%
  • 11.0%
  • 8.8%

Correct Answer: 10.4%

Q6. For desired concentration 6% from 4% and 10% solutions, what is the ratio of 4% to 10% using alligation?

  • 2:1
  • 1:2
  • 1:1
  • 4:3

Correct Answer: 2:1

Q7. Which formula represents the alligation method for two strengths C1 (lower), C2 (higher) and desired C?

  • Parts of C1 : C2 = (C2 − C) : (C − C1)
  • Parts of C1 : C2 = (C − C1) : (C2 − C)
  • Parts of C1 : C2 = (C1 − C) : (C − C2)
  • Parts of C1 : C2 = (C + C1) : (C2 + C)

Correct Answer: Parts of C1 : C2 = (C2 − C) : (C − C1)

Q8. A pharmacist needs 500 mL of 2% solution using 5% and 0.5% solutions. Using alligation, how much 5% solution is required?

  • 125 mL
  • 200 mL
  • 150 mL
  • 100 mL

Correct Answer: 125 mL

Q9. When mixing powders of 40% and 60% potency to get 52% potency, the parts of 40% to 60% are:

  • 8:12
  • 12:8
  • 2:3
  • 3:2

Correct Answer: 12:8

Q10. Alligation is particularly useful in pharmacy for which of the following tasks?

  • Calculating required proportions when compounding different strengths
  • Predicting chemical reaction rates
  • Determining drug bioavailability from first principles
  • Measuring osmolarity from freezing point depression only

Correct Answer: Calculating required proportions when compounding different strengths

Q11. Using alligation, to prepare 1 L of 7% solution from 5% and 12% solutions, what volumes of 12% solution are needed?

  • 285.7 mL
  • 714.3 mL
  • 200 mL
  • 400 mL

Correct Answer: 285.7 mL

Q12. If the desired concentration is equal to one of the component concentrations, alligation indicates:

  • Use only that component; the ratio includes zero parts of the other
  • A 1:1 ratio always
  • It is impossible to achieve
  • Need to dilute with ethanol

Correct Answer: Use only that component; the ratio includes zero parts of the other

Q13. A formulation requires 250 mg of active drug at 2% w/w using 5% and 1% powders. How many grams of 5% powder are needed? (Assume rest of weight is inert)

  • 1.25 g
  • 0.625 g
  • 2.5 g
  • 0.25 g

Correct Answer: 0.625 g

Q14. Alligation can be extended to three-component mixtures by:

  • Pairwise alligation and successive mixing or using weighted averages
  • Only using binary mixtures; three components are not possible
  • Mixing arbitrary amounts without calculation
  • Using Henderson-Hasselbalch equation only

Correct Answer: Pairwise alligation and successive mixing or using weighted averages

Q15. You have 2 solutions: 0.9% and 3% NaCl. To make 1 L of 1.2% NaCl, how many mL of 3% solution are needed?

  • 100 mL
  • 60 mL
  • 120 mL
  • 200 mL

Correct Answer: 60 mL

Q16. For desired concentration 25% using 10% and 40% solutions, the alligation parts of 10%:40% are:

  • 15:10
  • 10:15
  • 3:2
  • 2:3

Correct Answer: 15:10

Q17. When applying alligation to convert mg/mL concentrations, you must:

  • Ensure units are consistent before calculating ratios
  • Always convert to percentages first
  • Only use volumes in liters, not mL
  • Ignore units because ratios cancel out

Correct Answer: Ensure units are consistent before calculating ratios

Q18. A 0.5% solution is mixed with a 2% solution to obtain 1.25%. If total volume is 400 mL, how much 2% solution is used?

  • 160 mL
  • 240 mL
  • 200 mL
  • 100 mL

Correct Answer: 160 mL

Q19. The alligation method fails or is not applicable when:

  • The desired concentration lies outside the range of component concentrations
  • The desired concentration is between the two concentrations
  • Units are convertible
  • Components are miscible

Correct Answer: The desired concentration lies outside the range of component concentrations

Q20. Which of the following is an advantage of using alligation in pharmaceutical compounding?

  • Fast determination of mixing ratios without algebraic equations
  • Provides exact pH values for buffers
  • Predicts long-term stability data
  • Eliminates need for weighing

Correct Answer: Fast determination of mixing ratios without algebraic equations

Q21. A pharmacist mixes 150 mL of 3% solution with 50 mL of 9% solution. What is the final percent strength?

  • 4.5%
  • 5.25%
  • 4.0%
  • 3.75%

Correct Answer: 4.5%

Q22. Using alligation, what is the ratio of 2% to 8% solutions to make 5% solution?

  • 3:2
  • 2:3
  • 1:1
  • 5:3

Correct Answer: 3:2

Q23. To obtain 250 g of 18% ointment using 10% and 30% bases, how many grams of 30% base are needed?

  • 100 g
  • 125 g
  • 75 g
  • 150 g

Correct Answer: 100 g

Q24. Which step is essential before applying alligation to two solutions expressed in different units (e.g., mg/mL and % w/v)?

  • Convert both concentrations to the same unit system
  • Dilute both solutions to 1% first
  • Measure densities of both solutions
  • Freeze-dry the samples

Correct Answer: Convert both concentrations to the same unit system

Q25. If you need 100 mL of 4% solution and have 6% and 1% solutions, how much 6% solution is required?

  • 50 mL
  • 30 mL
  • 20 mL
  • 40 mL

Correct Answer: 30 mL

Q26. A compound requires mixing 2% and 14% to make 10%. The parts of 2%:14% are:

  • 4:8
  • 1:3
  • 3:1
  • 2:5

Correct Answer: 1:3

Q27. In preparing a target strength using alligation, the “difference” values used to form the ratio are:

  • Absolute differences between each component concentration and the desired concentration
  • Percent differences relative to the higher concentration only
  • Differences divided by total volume first
  • Squared differences to weight stronger components

Correct Answer: Absolute differences between each component concentration and the desired concentration

Q28. Which of the following describes a correct approach to three-component alligation sequential mixing?

  • Mix two components to get an intermediate concentration, then alligate that with the third
  • Alligate all three at once without conversions
  • Use only the strongest component and dilute accordingly
  • Apply Henderson-Hasselbalch equation instead

Correct Answer: Mix two components to get an intermediate concentration, then alligate that with the third

Q29. A technician has 4% and 16% solutions and needs 400 mL of 10%. How much 16% solution is needed?

  • 150 mL
  • 100 mL
  • 200 mL
  • 250 mL

Correct Answer: 100 mL

Q30. For exam preparation, why is practicing alligation MCQs particularly beneficial for B.Pharm students?

  • It improves speed, accuracy, and understanding of mixture and dilution problems commonly encountered in pharmacy
  • It replaces the need to learn other calculation methods
  • It guarantees perfect compounding without checks
  • It is only useful for theoretical exams, not practical work

Correct Answer: It improves speed, accuracy, and understanding of mixture and dilution problems commonly encountered in pharmacy

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