X-ray powder diffraction technique MCQs With Answer

X-ray Powder Diffraction Technique MCQs With Answer

X-ray powder diffraction (PXRD) is a cornerstone technique in Modern Pharmaceutical Analytical Techniques for identifying crystalline phases, assessing polymorphism, and quantifying crystallinity in drug substances and excipients. For M. Pharm students, mastering PXRD means understanding Bragg’s law, sample preparation, instrument geometry, and data interpretation strategies like Rietveld refinement. This quiz emphasizes real-world pharmaceutical applications—polymorph screening, preferred orientation control, amorphous content estimation, thin-film analysis, and minimizing artifacts such as fluorescence and zero-shift errors. The questions also touch on critical parameters such as wavelength selection, 2θ range, peak broadening analysis, and database-driven phase identification. Use this set to test and deepen your analytical skills for research and quality control environments.

Q1. Which fundamental relation explains the condition for constructive interference in powder XRD?

• Fresnel’s diffraction law
• Beer–Lambert law
• Bragg’s law (nλ = 2d sinθ)
• Snell’s law

Correct Answer: Bragg’s law (nλ = 2d sinθ)

Q2. The most commonly used laboratory radiation for pharmaceutical PXRD is:

• Mo Kα (λ ≈ 0.7093 Å)
• Cu Kα (λ ≈ 1.5406 Å)
• Co Kβ (λ ≈ 1.625 Å)
• UV light (254 nm)

Correct Answer: Cu Kα (λ ≈ 1.5406 Å)

Q3. The position of peaks in a PXRD pattern primarily provides information about:

• Crystallite size
• Interplanar spacing (d-spacing)
• Molecular weight
• Melting point

Correct Answer: Interplanar spacing (d-spacing)

Q4. In the Scherrer equation D = Kλ/(β cosθ), the term β represents:

• The instrumental slit divergence
• The 2θ peak position in degrees
• The full width at half maximum (FWHM) in radians, corrected for instrumental broadening
• The linear absorption coefficient of the sample

Correct Answer: The full width at half maximum (FWHM) in radians, corrected for instrumental broadening

Q5. The Scherrer equation most directly relates peak broadening to which material parameter?

• Crystallite size
• Lattice parameter a
• Moisture content
• Thermal conductivity

Correct Answer: Crystallite size

Q6. Which sample preparation method best reduces preferred orientation in flat-plate PXRD of pharmaceutical powders?

• Front pressing with a smooth glass slide
• Back-loading (or side-drifting) the sample into the holder
• Using a strong magnet during loading
• Freeze-drying the sample prior to analysis

Correct Answer: Back-loading (or side-drifting) the sample into the holder

Q7. When distinguishing polymorphs of an API by PXRD, the most diagnostic pattern changes are:

• Only baseline shifts without peak movement
• Changes in peak positions and relative intensities
• Only narrower peak widths
• Complete absence of peaks

Correct Answer: Changes in peak positions and relative intensities

Q8. A commonly used internal standard for quantitative phase analysis and zero-shift correction in PXRD is:

• Sodium chloride (NaCl)
• Corundum (α-Al2O3)
• Sucrose
• Graphite

Correct Answer: Corundum (α-Al2O3)

Q9. A practical approach to estimate percent crystallinity of a semi-crystalline pharmaceutical solid from PXRD data is to:

• Use DSC enthalpy values only
• Integrate crystalline peak area relative to total area (crystalline peaks + amorphous halo) after background subtraction
• Measure only the highest-intensity peak height
• Track the color change of the powder

Correct Answer: Integrate crystalline peak area relative to total area (crystalline peaks + amorphous halo) after background subtraction

Q10. Grazing-incidence XRD (GIXRD) is primarily used for:

• Bulk powders in reflection geometry
• Thin films and surface-sensitive analysis
• Gaseous samples at low pressure
• Crystallization kinetics in solution

Correct Answer: Thin films and surface-sensitive analysis

Q11. For routine phase identification of pharmaceutical powders using Cu Kα radiation, a typical 2θ scan range is:

• 0–5°
• 5–40°
• 60–120°
• 150–180°

Correct Answer: 5–40°

Q12. In a Cu-based PXRD setup, a nickel (Ni) filter is primarily employed to suppress:

• Cu Kα1 radiation
• Cu Kβ radiation
• All scattering from the sample
• Ambient humidity effects

Correct Answer: Cu Kβ radiation

Q13. The standard database used globally for phase identification from powder patterns is the:

• NMRShiftDB
• ICDD Powder Diffraction File (PDF)
• PubChem Compound database
• Protein Data Bank (PDB)

Correct Answer: ICDD Powder Diffraction File (PDF)

Q14. In Bragg–Brentano geometry used for most laboratory PXRD, the specimen is mounted as a:

• Flat plate in reflection
• Capillary in transmission
• Thin film on a TEM grid
• Liquid jet between windows

Correct Answer: Flat plate in reflection

Q15. A common cause of systematic 2θ peak shifts in flat-plate PXRD measurements is:

• Detector dead-time losses
• Sample height displacement relative to the focusing circle
• Random counting noise
• Minor preferred orientation

Correct Answer: Sample height displacement relative to the focusing circle

Q16. To mitigate strong sample fluorescence when analyzing Fe-containing excipients with Cu radiation, one effective strategy is to:

• Increase tube current substantially
• Switch to Co Kα radiation (λ ≈ 1.789 Å)
• Remove the monochromator
• Use a broader receiving slit

Correct Answer: Switch to Co Kα radiation (λ ≈ 1.789 Å)

Q17. Under good counting statistics and proper sample preparation, the approximate detection limit for a minor crystalline phase by PXRD is:

• 0.0001 wt%
• 0.5–1 wt%
• 10 wt%
• 50 wt%

Correct Answer: 0.5–1 wt%

Q18. Rietveld refinement for pharmaceutical PXRD data primarily involves:

• Fitting only the top five highest peaks
• Full-profile least-squares refinement using a crystal structure model
• Background subtraction without peak modeling
• Qualitative comparison by visual overlay alone

Correct Answer: Full-profile least-squares refinement using a crystal structure model

Q19. The primary function of a sample spinner in a powder diffractometer is to:

• Cool the sample to prevent degradation
• Randomize crystallite orientation and improve counting statistics
• Generate Kα1 and Kα2 lines
• Align the X-ray source focus

Correct Answer: Randomize crystallite orientation and improve counting statistics

Q20. An amorphous pharmaceutical material typically exhibits in its PXRD pattern:

• Numerous sharp, intense Bragg peaks
• A broad diffuse halo with no sharp peaks
• Negative intensity values at high angles
• Only Kβ radiation signatures

Correct Answer: A broad diffuse halo with no sharp peaks

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