GPAT practice: Pharmaceutics and dosage forms
20 original GPAT-style questions on physical pharmacy, tablets, capsules, parenterals, disperse systems and novel drug delivery with answers and explanations. Tap an option to check your answer, or open "Show answer".
1. A weak acid has pKa 4.4. In a solution of pH 5.4, what is the approximate ratio of ionised to unionised form?
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Answer: B — By Henderson–Hasselbalch, pH − pKa = log([ionised]/[unionised]) = 1, so the ratio is 10 : 1.
2. A Newtonian liquid is one in which viscosity
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Answer: C — Newtonian flow shows shear stress directly proportional to shear rate, so viscosity is constant. The other options describe pseudoplastic, dilatant and thixotropic behaviour.
3. Thixotropy is best described as
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Answer: A — Thixotropic systems thin under shear and rebuild their structure slowly on standing. Option B is dilatancy and option C is plastic flow.
4. A powder has bulk density 0.40 g/mL and tapped density 0.50 g/mL. Its Carr's compressibility index is
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Answer: C — Carr's index = (tapped − bulk)/tapped × 100 = (0.10/0.50) × 100 = 20 %. Using bulk density in the denominator would wrongly give 25 %.
5. Which angle of repose generally indicates excellent powder flow?
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Answer: A — A lower angle of repose reflects less interparticle friction and better flow; values above about 40° indicate poor flow.
6. According to the Noyes–Whitney equation, the dissolution rate of a drug increases with
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Answer: B — Dissolution rate is proportional to surface area, diffusion coefficient and concentration gradient, and inversely proportional to diffusion-layer thickness. Micronisation therefore raises the rate.
7. Which of the following is a superdisintegrant used in tablets?
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Answer: B — Croscarmellose sodium, sodium starch glycolate and crospovidone are superdisintegrants. PVP is a binder, while magnesium stearate and talc are lubricant/glidant.
8. Capping in tablets is most commonly associated with
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Answer: B — Air trapped in fines is released on ejection and splits the tablet cap off. It is reduced by lowering fines, using pre-compression and reducing compression speed.
9. Cellulose acetate phthalate is used mainly as
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Answer: D — It is insoluble in gastric fluid but dissolves at higher intestinal pH, protecting acid-labile drugs or the stomach from irritant drugs.
10. Among the standard hard gelatin capsule sizes, which holds the largest fill volume?
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Answer: D — Size 000 is the largest and size 5 the smallest of the standard human-use sizes; capacity decreases in the order 000 > 00 > 0 > 1 > 2 > 3 > 4 > 5.
11. Which sodium chloride concentration is isotonic with blood and lachrymal fluid?
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Answer: B — Normal saline is 0.9 % w/v NaCl (about 286–308 mOsm/L), isotonic with plasma. A 5 % solution would be hypertonic.
12. Which method is appropriate for depyrogenation of glassware?
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Answer: C — Bacterial endotoxins are heat-stable and survive steam sterilisation and sterile filtration; dry heat at about 250 °C destroys them.
13. According to Bancroft's rule, an emulsifier that is more soluble in water tends to produce
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Answer: B — The phase in which the emulsifier is more soluble becomes the continuous phase, so a hydrophilic emulsifier gives o/w emulsions.
14. Which change in an emulsion is irreversible and cannot be corrected by simple shaking?
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Answer: C — Cracking is coalescence with permanent separation of the phases. Creaming and flocculation are reversible by shaking.
15. According to Stokes' law, the sedimentation velocity of a spherical particle is directly proportional to
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Answer: B — v = d²(ρs − ρm)g / 18η, so velocity varies with the square of diameter and inversely with viscosity.
16. Compared with a deflocculated suspension, a flocculated suspension typically shows
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Answer: B — Flocs settle quickly but form a loose sediment that is easily redispersed, whereas deflocculated particles settle slowly into a hard cake.
17. Zeta potential is the electric potential
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Answer: B — Zeta potential is measured at the slipping plane and indicates the stability of colloidal dispersions: a low value favours flocculation.
18. Liposomes are best described as
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Answer: A — Hydrophilic drugs are held in the aqueous core, lipophilic drugs within the bilayer.
19. Which property favours passive transdermal delivery of a drug?
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Answer: B — Low molecular weight (generally under 500 Da) and balanced lipophilicity allow passage across the stratum corneum, the main barrier.
20. For a drug released from an insoluble matrix by diffusion, the Higuchi model predicts that the amount released is proportional to
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Answer: B — Higuchi's equation gives Q = k√t for matrix systems, as opposed to zero-order (proportional to time) release from reservoir or osmotic systems.