Applications of X-ray diffraction MCQs With Answer

Applications of X-ray Diffraction MCQs With Answer helps M. Pharm students master how X-ray diffraction (XRD) supports drug development, characterization, and quality control. From identifying polymorphs and co-crystals to quantifying crystallinity and monitoring solid-state stability, XRD is central to modern pharmaceutical analytical techniques. This quiz focuses on practical decision-making: choosing PXRD versus SCXRD, interpreting peak shifts, handling mixtures and preferred orientation, and applying Rietveld refinement, Williamson–Hall analysis, and GIXRD. You’ll also explore real-world scenarios such as hydrate/solvate detection, milling-induced amorphization, tablet compression effects, and regulatory expectations (ICH). Use these MCQs to deepen understanding of solid-state analysis and build confidence in applying XRD to formulation, manufacturing, and quality-by-design workflows.

Q1. In pharmaceutical solids, the principal application of powder X-ray diffraction (PXRD) is:

• Assessing molecular weight distribution in polymers
• Identification and quantification of polymorphic forms of APIs
• Measuring residual organic solvents directly
• Determining particle shape by imaging

Correct Answer: Identification and quantification of polymorphic forms of APIs

Q2. For unambiguous determination of a drug’s 3D molecular structure and absolute configuration, the preferred X-ray method is:

• PXRD with Rietveld refinement
• Single-crystal X-ray diffraction (SCXRD)
• Grazing-incidence XRD (GIXRD)
• Small-angle X-ray scattering (SAXS)

Correct Answer: Single-crystal X-ray diffraction (SCXRD)

Q3. In PXRD, information primarily derived from peak positions (2θ) rather than intensities is:

• Crystallite size distribution
• Preferred orientation in pressed compacts
• Interplanar spacing and phase identification
• Microstrain quantification

Correct Answer: Interplanar spacing and phase identification

Q4. During dehydration of a crystalline hydrate, the loss of lattice water typically causes what change in the PXRD pattern?

• Peak positions shift to higher 2θ due to decreased d-spacing
• Peak positions shift to lower 2θ due to increased d-spacing
• Only peak intensities change; positions are invariant
• Appearance of a broad amorphous halo without peak shifts

Correct Answer: Peak positions shift to higher 2θ due to decreased d-spacing

Q5. The most robust approach to quantify percent crystallinity in a semi-crystalline pharmaceutical polymer by PXRD is:

• Visual comparison of peak heights to the amorphous halo
• PXRD with internal amorphous standard and Rietveld refinement
• Using a single diffraction peak area as a proxy
• Measuring density and correlating with crystallinity

Correct Answer: PXRD with internal amorphous standard and Rietveld refinement

Q6. To confirm the polymorphic form of an API within a tablet containing diffracting excipients, the best strategy is:

• Record PXRD and compare only the highest-intensity peak
• Extract the API by solvent and run PXRD on the residue only
• Whole-pattern fitting (Rietveld) using reference patterns with preferred orientation correction
• Use UV-Vis spectroscopy to avoid overlap

Correct Answer: Whole-pattern fitting (Rietveld) using reference patterns with preferred orientation correction

Q7. Milling an API to increase dissolution often increases amorphous content. Which PXRD signature indicates this change?

• Narrower peaks with increased intensity
• Appearance of new sharp peaks at low angles
• Peak broadening, reduced peak intensity, and a more pronounced diffuse halo
• No change in diffractogram

Correct Answer: Peak broadening, reduced peak intensity, and a more pronounced diffuse halo

Q8. Regarding distinguishing salts from co-crystals using X-ray diffraction in pharmaceuticals:

• PXRD alone definitively distinguishes salt versus co-crystal
• SCXRD can locate protons and definitively identify salt versus co-crystal
• IR spectroscopy is superior to all XRD methods for this purpose
• SAXS is the gold standard for salt determination

Correct Answer: SCXRD can locate protons and definitively identify salt versus co-crystal

Q9. Which sample preparation minimizes preferred orientation for platy or needle-like crystals in PXRD?

• Front-loading into a flat holder with pressing
• Back-loading with minimal pressure and spinning the stage during acquisition
• Mounting as a smooth film without rotation
• Using a fixed-stage setup without spinning

Correct Answer: Back-loading with minimal pressure and spinning the stage during acquisition

Q10. Which ICH guideline addresses specifications (including identity tests) for drug substances and products, under which XRPD may serve as an identification test?

• ICH Q3C
• ICH Q6A
• ICH Q2(R2)
• ICH Q1A(R2)

Correct Answer: ICH Q6A

Q11. The most commonly used X-ray tube target for laboratory PXRD of organic pharmaceutical solids is:

• Chromium (Cr Kα)
• Molybdenum (Mo Kα)
• Copper (Cu Kα)
• Silver (Ag Kα)

Correct Answer: Copper (Cu Kα)

Q12. To quantify a minor polymorph present at ~1% w/w within a major form using PXRD, the best practice is to:

• Integrate a single diagnostic peak and assume linearity
• Use an internal standard and construct a calibration curve with mixtures; apply whole-pattern fitting
• Increase scan speed to reduce noise
• Rely on visual inspection of shoulder peaks

Correct Answer: Use an internal standard and construct a calibration curve with mixtures; apply whole-pattern fitting

Q13. To decouple crystallite size and microstrain contributions to line broadening in pharmaceutical PXRD, you would use:

• Rietveld scale factor analysis
• Le Bail fitting
• Williamson–Hall analysis
• Debye–Scherrer formula alone

Correct Answer: Williamson–Hall analysis

Q14. In stability studies, in situ variable temperature–humidity PXRD is especially useful for:

• Measuring assay of the API
• Monitoring real-time hydrate/solvate formation and solid–solid phase transitions
• Determining dissolution rate directly
• Quantifying residual metals

Correct Answer: Monitoring real-time hydrate/solvate formation and solid–solid phase transitions

Q15. To reduce preferred orientation effects when analyzing compressed tablets by XRD, a suitable approach is:

• Reflection geometry with strong surface pressing
• Transmission Debye–Scherrer capillary geometry with sample spinning
• Static reflection mode without spinning
• Increase tube voltage only

Correct Answer: Transmission Debye–Scherrer capillary geometry with sample spinning

Q16. Which statement about amorphous pharmaceutical solids and PXRD is accurate?

• PXRD can solve the long-range crystal structure of amorphous materials
• PXRD shows a broad halo for amorphous phases; quantification often requires external or internal standards
• Amorphous phases produce sharper peaks than crystalline phases
• PXRD cannot detect amorphous content at all

Correct Answer: PXRD shows a broad halo for amorphous phases; quantification often requires external or internal standards

Q17. To analyze crystalline APIs in thin film coatings on tablets or substrates, the most appropriate XRD configuration is:

• High-temperature XRD
• Grazing-incidence XRD (GIXRD)
• Single-crystal XRD
• SAXS

Correct Answer: Grazing-incidence XRD (GIXRD)

Q18. For characterizing short-range order in amorphous APIs and disordered co-amorphous systems using X-rays, the recommended method is:

• Conventional PXRD only
• Total scattering with pair distribution function (PDF) analysis
• GIXRD at low incident angles
• Energy-dispersive XRD

Correct Answer: Total scattering with pair distribution function (PDF) analysis

Q19. When quantifying multiple crystalline phases in an API–excipient mixture with extensive peak overlap, the preferred PXRD approach is:

• Reference intensity ratio (RIR) using a single line
• Rietveld refinement with whole-pattern fitting
• Manual subtraction of the excipient pattern
• Peak height ratio method only

Correct Answer: Rietveld refinement with whole-pattern fitting

Q20. In developing an amorphous solid dispersion (ASD) of an API with a polymer, which PXRD observation best supports successful amorphization?

• Retention of sharp API Bragg peaks with slightly reduced intensity
• Complete absence of API Bragg peaks and presence of a broad diffuse halo
• Appearance of new sharp peaks not present in either component
• Shift of a single API peak by ~0.1° 2θ

Correct Answer: Complete absence of API Bragg peaks and presence of a broad diffuse halo

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