Types of crystals MCQs With Answer

Types of crystals is a cornerstone topic in Modern Pharmaceutical Analytical Techniques because crystal form directly controls solubility, stability, bioavailability, manufacturability, and regulatory acceptance of drug substances. In this concise blog, we revisit how crystals are classified—by bonding (ionic, molecular, metallic, covalent network), by symmetry (seven crystal systems, 14 Bravais lattices), and by pharmaceutical relevance (polymorphs, hydrates/solvates, co-crystals, racemates, amorphous). You’ll also connect key analytical tools (PXRD, DSC, IR) to decisions about form selection and control. The 20 MCQs that follow are designed for M. Pharm students to test understanding beyond definitions—probing relationships like enantiotropy vs monotropy, pseudopolymorphism, Z value, habit vs lattice, and how crystallization conditions drive the formation and performance of crystal forms.

Q1. Which statement best describes polymorphism in pharmaceutical solids?

• Existence of a compound in multiple crystalline forms with the same chemical composition but different lattice arrangements
• Existence in different chemical forms (salts) with the same crystal lattice
• Transformation of a crystalline solid into an amorphous solid
• Existence in multiple hydrates only

Correct Answer: Existence of a compound in multiple crystalline forms with the same chemical composition but different lattice arrangements

Q2. Which of the following is NOT one of the seven crystal systems?

• Triclinic
• Monoclinic
• Isotropic
• Tetragonal

Correct Answer: Isotropic

Q3. How many distinct Bravais lattices exist in three dimensions?

• 7
• 14
• 32
• 230

Correct Answer: 14

Q4. Which pairing correctly matches a crystal type with its typical property?

• Ionic crystals: good electrical conductivity as solids
• Molecular crystals: low melting points and often volatile
• Metallic crystals: brittle and insulating
• Covalent network crystals: readily soluble in polar solvents

Correct Answer: Molecular crystals: low melting points and often volatile

Q5. A crystal containing stoichiometric water integrated into its lattice is best termed a:

• Hydrate
• Solvate
• Co-crystal
• Clathrate

Correct Answer: Hydrate

Q6. In an enantiotropic polymorphic pair, which statement is true?

• One form is stable at all temperatures below the melting point of both forms
• The forms are related by a reversible transition at a defined transition temperature below melting
• The metastable form always has a lower melting point than the stable form
• Only one polymorph can be isolated under ambient conditions

Correct Answer: The forms are related by a reversible transition at a defined transition temperature below melting

Q7. Which analytical technique most directly distinguishes between different crystal lattices of the same compound?

• Powder X-ray diffraction (PXRD)
• UV–Visible spectroscopy
• HPLC retention time
• pH measurement

Correct Answer: Powder X-ray diffraction (PXRD)

Q8. The term “crystal habit” refers to the:

• External shape determined by relative growth rates of crystal faces
• Internal arrangement of atoms within the unit cell
• Presence of dislocations and vacancies
• Thermal behavior observed in DSC

Correct Answer: External shape determined by relative growth rates of crystal faces

Q9. Which best describes a racemic conglomerate?

• A 1:1 mixture of enantiomers crystallizing as separate enantiomerically pure crystals
• A crystal where both enantiomers are incorporated in the same lattice with 1:1 stoichiometry
• A solid solution of enantiomers with variable composition
• A co-crystal of an enantiomer with an achiral co-former

Correct Answer: A 1:1 mixture of enantiomers crystallizing as separate enantiomerically pure crystals

Q10. In crystallography, Z denotes the:

• Number of molecules per asymmetric unit
• Number of formula units per unit cell
• Number of symmetry operations in the space group
• Number of unique reflections in a PXRD pattern

Correct Answer: Number of formula units per unit cell

Q11. Cubic close packing (ccp) corresponds to which Bravais lattice?

• Face-centered cubic (FCC)
• Body-centered cubic (BCC)
• Simple cubic (P)
• Hexagonal primitive (P)

Correct Answer: Face-centered cubic (FCC)

Q12. A defining feature of an amorphous solid is:

• Absence of long-range order in atomic/molecular arrangement
• A sharp, invariant melting point
• Presence of distinct Bragg peaks in PXRD
• Ease of growing single crystals

Correct Answer: Absence of long-range order in atomic/molecular arrangement

Q13. Which of the following is a point defect in crystals?

• Vacancy
• Edge dislocation
• Grain boundary
• Stacking fault

Correct Answer: Vacancy

Q14. Pseudopolymorphism in pharmaceuticals refers to:

• Formation of different crystalline forms due to inclusion of solvent molecules (hydrates/solvates)
• Crystallization of different salt forms of an API
• Production of amorphous solid dispersions
• Reduction of particle size without changing crystal structure

Correct Answer: Formation of different crystalline forms due to inclusion of solvent molecules (hydrates/solvates)

Q15. Ostwald’s Rule of Stages implies that during crystallization:

• The most stable polymorph forms first under kinetic control
• Crystallization often proceeds via metastable forms before the most stable polymorph
• All polymorphs form simultaneously at equal rates
• Only amorphous intermediates appear before crystallization

Correct Answer: Crystallization often proceeds via metastable forms before the most stable polymorph

Q16. Which of the following is a classic example of a covalent network crystal?

• Diamond
• Sodium chloride
• Camphor
• Ice

Correct Answer: Diamond

Q17. Which crystal habit most commonly leads to poor flowability and tableting problems?

• Needle-like (acicular)
• Equant
• Spherical
• Blocky prismatic

Correct Answer: Needle-like (acicular)

Q18. For an enantiotropic polymorphic pair, the transition temperature (Ttr) must be:

• Below the melting points of both polymorphs
• Above the melting points of both polymorphs
• Equal to the melting point of the stable form
• Unrelated to melting behavior

Correct Answer: Below the melting points of both polymorphs

Q19. For the same compound at a given temperature, which polymorph typically shows higher apparent solubility?

• The metastable form
• The most stable form
• All polymorphs have identical solubility
• Only solvated forms

Correct Answer: The metastable form

Q20. Which factor most strongly promotes formation of a crystalline solvate during crystallization?

• Solvent’s ability to hydrogen bond and its molecular size/shape fitting lattice voids
• Particle morphology of the seed crystals
• Grinding time during milling
• Capsule shell composition

Correct Answer: Solvent’s ability to hydrogen bond and its molecular size/shape fitting lattice voids

Q21. A pharmaceutical co-crystal is best defined as:

• A multi-component crystalline material composed of neutral molecules in a defined stoichiometric ratio held by non-covalent interactions
• A salt formed by proton transfer between API and counterion
• A crystalline solvate with included solvent molecules
• A physical mixture of separate crystalline powders

Correct Answer: A multi-component crystalline material composed of neutral molecules in a defined stoichiometric ratio held by non-covalent interactions

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