Electron microscopy MCQs With Answer

Electron microscopy MCQs With Answer offers B. Pharm students a focused, SEO-friendly introduction to transmission and scanning electron microscopy, sample preparation, contrast mechanisms, and pharmaceutical applications like nanoparticle characterization and drug delivery imaging. This concise guide covers key concepts — TEM, SEM, cryo-EM, staining, ultramicrotomy, accelerating voltage, resolution, detectors and EDS — with clear terminology useful for exam prep and lab work. Questions emphasize practical protocols, artifacts, instrument settings and interpretation of micrographs relevant to formulation and quality control. Designed for B. Pharm curricula, these MCQs help reinforce theory and lab skills in imaging-based pharmaceutical analysis. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which electron microscope is most suitable for detailed internal ultrastructure of cells and thin sections?

• Scanning electron microscope
• Transmission electron microscope
• Atomic force microscope
• Light microscope

Correct Answer: Transmission electron microscope

Q2. In SEM imaging, which signal primarily provides high surface topography contrast?

• Backscattered electrons
• Secondary electrons
• Characteristic X-rays
• Transmitted electrons

Correct Answer: Secondary electrons

Q3. Which staining reagent is commonly used to increase electron density of lipids and membranes in TEM?

• Lead citrate
• Osmium tetroxide
• Uranyl acetate
• Silver nitrate

Correct Answer: Osmium tetroxide

Q4. What is the primary purpose of sputter coating non-conductive samples before SEM?

• To reduce vacuum pressure
• To increase electrical conductivity and reduce charging
• To fix biological structures chemically
• To improve chemical composition analysis by EDS

Correct Answer: To increase electrical conductivity and reduce charging

Q5. Which parameter most directly limits theoretical resolution in electron microscopy?

• Numerical aperture of objective lens
• Wavelength of electrons
• Specimen thickness
• Detector pixel size

Correct Answer: Wavelength of electrons

Q6. Which electron source provides the highest brightness and best spatial resolution in modern EMs?

• Tungsten filament
• LaB6 filament
• Cold field emission gun
• Thermionic cathode

Correct Answer: Cold field emission gun

Q7. In TEM, what is the role of the objective aperture?

• To accelerate electrons to higher energy
• To select central beam for diffraction only
• To improve image contrast by limiting scattered electrons
• To cool the sample during imaging

Correct Answer: To improve image contrast by limiting scattered electrons

Q8. Which technique allows elemental analysis combined with SEM imaging?

• Energy-dispersive X-ray spectroscopy (EDS)
• Selected area electron diffraction (SAED)
• Electron energy loss spectroscopy (EELS)
• Atomic absorption spectroscopy

Correct Answer: Energy-dispersive X-ray spectroscopy (EDS)

Q9. What causes “beam damage” in biological samples during TEM?

• Excessive vacuum
• High electron dose causing radiolysis and heating
• Use of conductive coating
• Low accelerating voltage

Correct Answer: High electron dose causing radiolysis and heating

Q10. Which embedding resin is commonly used for ultramicrotomy of biological samples?

• Polystyrene
• Epoxy resin (e.g., Epon/Araldite)
• Polyethylene glycol
• Gelatin

Correct Answer: Epoxy resin (e.g., Epon/Araldite)

Q11. In TEM, what does SAED (selected area electron diffraction) primarily provide?

• Surface topography
• Elemental composition
• Crystallographic information
• Thickness measurement

Correct Answer: Crystallographic information

Q12. Which contrast mechanism is most important for imaging unstained biological specimens in TEM under cryo conditions?

• Mass-thickness contrast
• Z-contrast from heavy metals
• Phase contrast
• Backscattered electron contrast

Correct Answer: Phase contrast

Q13. What is the typical accelerating voltage range used for high-resolution TEM of nanoparticles?

• 0.5–5 kV
• 20–300 kV
• 1–5 MV
• 5–15 kV

Correct Answer: 20–300 kV

Q14. Which grid support film is commonly used for TEM biological samples to reduce contamination and provide support?

• Aluminum foil
• Formvar or carbon-coated copper grids
• Glass coverslips
• Plastic Petri dish

Correct Answer: Formvar or carbon-coated copper grids

Q15. Negative staining in TEM primarily improves visibility of which kind of specimens?

• Thick resin-embedded sections
• Surface topography of metals
• Small biological particles like viruses and proteins
• Bulk crystals for diffraction

Correct Answer: Small biological particles like viruses and proteins

Q16. Which heavy metal stain binds strongly to nucleic acids and proteins in TEM?

• Lead citrate
• Uranyl acetate
• Phosphotungstic acid
• Osmium tetroxide

Correct Answer: Uranyl acetate

Q17. In SEM, an increase in accelerating voltage typically results in:

• Reduced penetration depth and shallower interaction volume
• Larger interaction volume and deeper specimen penetration
• No change in interaction volume
• Immediate sample vitrification

Correct Answer: Larger interaction volume and deeper specimen penetration

Q18. Which detector in SEM is best for atomic number (Z) contrast imaging?

• Secondary electron detector
• Backscattered electron detector
• Thermionic detector
• Scanning tunneling detector

Correct Answer: Backscattered electron detector

Q19. In TEM sample prep, what is the purpose of ultramicrotomy?

• To coat samples with metal
• To cut ultrathin sections (~50–100 nm) for transmission
• To freeze-dry samples
• To perform elemental mapping

Correct Answer: To cut ultrathin sections (~50–100 nm) for transmission

Q20. Cryo-EM is particularly valuable because it:

• Requires no vacuum
• Preserves native hydrated state by rapid vitrification
• Uses only visible light
• Eliminates the need for detectors

Correct Answer: Preserves native hydrated state by rapid vitrification

Q21. Which artifact is commonly introduced by chemical fixation with glutaraldehyde?

• Vitrification
• Cross-linking induced shrinkage or masking of antigenic sites
• Increased electrical conductivity
• Enhanced crystal diffraction

Correct Answer: Cross-linking induced shrinkage or masking of antigenic sites

Q22. In EDS analysis, the Kα peak corresponds to:

• A type of backscattered electron
• Characteristic X-ray from electron transitions to the K shell
• Secondary electron emission
• Ultraviolet fluorescence

Correct Answer: Characteristic X-ray from electron transitions to the K shell

Q23. Which factor improves depth of field in SEM images?

• Low working distance and high accelerating voltage
• High condenser aperture and low magnification
• Large depth of field is intrinsic and cannot be changed
• Long working distance and small aperture (low probe size)

Correct Answer: Long working distance and small aperture (low probe size)

Q24. What is the main advantage of direct electron detectors (DED) in TEM/cryo-EM?

• They are cheaper than CCDs
• Higher detective quantum efficiency and faster frame rates
• They eliminate the need for alignment
• They work at atmospheric pressure

Correct Answer: Higher detective quantum efficiency and faster frame rates

Q25. Which process is used to prepare vitreous ice for cryo-EM grids?

• Slow air-drying at room temperature
• Chemical dehydration with ethanol
• Rapid plunge-freezing into liquid ethane or ethane/propane
• Freeze-drying with acetone

Correct Answer: Rapid plunge-freezing into liquid ethane or ethane/propane

Q26. In TEM, contrast due to atomic number differences (Z-contrast) is most prominent in which imaging mode?

• Bright-field imaging
• Dark-field imaging or high-angle annular dark-field (HAADF) in STEM
• Secondary electron imaging
• Optical microscopy

Correct Answer: Dark-field imaging or high-angle annular dark-field (HAADF) in STEM

Q27. What is “charging” in SEM and how is it minimized?

• Charging is detector overload and is minimized by turning off detectors
• Charging is electron accumulation on insulating samples, minimized by conductive coating or low vacuum
• Charging is caused by too much staining and fixed by washing
• Charging is sample electrification due to ions and is minimized by helium gas

Correct Answer: Charging is electron accumulation on insulating samples, minimized by conductive coating or low vacuum

Q28. Which microscope mode is best for measuring particle size distributions of pharmaceutical nanoparticles in dry state?

• Bright-field optical microscopy
• Transmission electron microscopy
• Scanning electron microscopy
• Light scattering techniques only

Correct Answer: Scanning electron microscopy

Q29. In TEM imaging, what does “defocus” primarily influence?

• The vacuum level
• The contrast transfer function and phase contrast
• The elemental composition
• The grid mesh size

Correct Answer: The contrast transfer function and phase contrast

Q30. Which resin property is most critical for good ultrathin sectioning?

• High electrical conductivity
• Appropriate hardness and polymerization for smooth cutting
• High solubility in water
• Magnetic susceptibility

Correct Answer: Appropriate hardness and polymerization for smooth cutting

Q31. What is a common use of immunogold labeling in electron microscopy for pharmacy research?

• To increase section thickness
• To localize specific proteins or antigens with electron-dense gold particles
• To coat grids for conductivity
• To calibrate magnification

Correct Answer: To localize specific proteins or antigens with electron-dense gold particles

Q32. Which EM technique allows 3D reconstruction of cellular volumes via serial sectioning or tomography?

• Selected area electron diffraction
• Electron tomography or serial block-face SEM
• EDS mapping
• Secondary ion mass spectrometry

Correct Answer: Electron tomography or serial block-face SEM

Q33. Why is glow-discharge treatment applied to TEM grids before sample application?

• To sterilize the grid only
• To make the carbon film hydrophilic and improve sample spreading
• To deposit metal coating
• To reduce mesh openings

Correct Answer: To make the carbon film hydrophilic and improve sample spreading

Q34. In SEM, what does lowering probe current generally achieve?

• Higher signal-to-noise ratio
• Less beam damage and lower signal
• Faster imaging
• Improved elemental sensitivity for EDS

Correct Answer: Less beam damage and lower signal

Q35. Which technique is useful to examine crystalline lattice fringes and interplanar spacing in nanoparticles?

• Low-magnification SEM
• High-resolution TEM (HRTEM)
• Optical polarized light microscopy
• Confocal microscopy

Correct Answer: High-resolution TEM (HRTEM)

Q36. What is the primary limitation when using TEM for routine quality control in manufacturing?

• Insufficient magnification
• Time-consuming sample preparation and limited throughput
• Inability to detect nanoparticles
• Too high automation

Correct Answer: Time-consuming sample preparation and limited throughput

Q37. Which gas is often used in variable-pressure SEM modes to reduce charging on non-conductive samples?

• Argon
• Nitrogen
• Water vapor or nitrogen/air mixture
• Helium

Correct Answer: Water vapor or nitrogen/air mixture

Q38. Which parameter must be controlled to minimize contamination buildup on TEM samples during imaging?

• Sample tilt only
• Electron dose and vacuum cleanliness
• Grid mesh size
• Type of embedding resin exclusively

Correct Answer: Electron dose and vacuum cleanliness

Q39. In STEM mode, what advantage does scanning provide over conventional TEM imaging?

• It removes the need for vacuum
• It allows simultaneous imaging and analytical techniques like EELS/EDS at high spatial resolution
• It uses light instead of electrons
• It increases sample thickness requirements

Correct Answer: It allows simultaneous imaging and analytical techniques like EELS/EDS at high spatial resolution

Q40. For EDS quantitative analysis, which factor must be considered to obtain accurate elemental concentrations?

• Only detector brand
• Sample thickness, geometry, and standards for matrix corrections
• Only accelerating voltage
• Only the specimen color

Correct Answer: Sample thickness, geometry, and standards for matrix corrections

Q41. Which sample preparation step reduces ice crystal formation during cryo-EM?

• Slow freezing at −20 °C
• Addition of heavy metal stains
• Rapid vitrification (plunge freezing) to avoid crystallization
• Air drying on the grid

Correct Answer: Rapid vitrification (plunge freezing) to avoid crystallization

Q42. Which type of electron scattering is mainly responsible for image contrast in TEM bright-field images?

• Elastic scattering and phase shifts of transmitted electrons
• Inelastic scattering producing X-rays
• Secondary electron emission only
• Magnetic scattering only

Correct Answer: Elastic scattering and phase shifts of transmitted electrons

Q43. Which maintenance step is critical for achieving stable high-resolution imaging in field emission microscopes?

• Regular replacement of specimen grids
• Maintaining ultra-high vacuum and tip cleaning/conditioning
• Frequent change of lenses
• Daily calibration of mesh size

Correct Answer: Maintaining ultra-high vacuum and tip cleaning/conditioning

Q44. What does “mean free path” of electrons in a specimen refer to?

• The average distance electrons travel in vacuum
• The average distance between atomic nuclei
• The average distance an electron travels in the specimen before inelastic scattering
• The maximum penetration depth of X-rays

Correct Answer: The average distance an electron travels in the specimen before inelastic scattering

Q45. Which coating material is commonly used to improve conductivity for SEM imaging of biological samples?

• Gold or gold-palladium alloy
• Silver nitrate solution
• Lead acetate
• Graphite powder only

Correct Answer: Gold or gold-palladium alloy

Q46. In electron diffraction, interplanar spacing d can be calculated using which relationship conceptually?

• Bragg’s law relating wavelength, angle, and d-spacing
• Ohm’s law for resistance
• Beer–Lambert law for absorbance
• Arrhenius equation for rates

Correct Answer: Bragg’s law relating wavelength, angle, and d-spacing

Q47. Which approach helps reduce charging and beam damage when imaging polymers or biological specimens in SEM?

• Use of highest possible accelerating voltage
• Coating with conductive film and using low accelerating voltage or low vacuum
• Immersing the sample in water during imaging
• Using visible light to pre-irradiate the sample

Correct Answer: Coating with conductive film and using low accelerating voltage or low vacuum

Q48. What is the main benefit of using HAADF-STEM for nanoparticle analysis?

• It provides chemical composition without spatial resolution
• It yields Z-contrast where intensity scales roughly with atomic number
• It only detects secondary electrons
• It eliminates the need for ultrathin sections

Correct Answer: It yields Z-contrast where intensity scales roughly with atomic number

Q49. Which common artifact arises from heavy metal staining when preparing TEM samples?

• Grid vitrification artifacts
• Precipitation of stain causing granular deposits that may obscure structures
• Complete removal of membranes
• Increased electrical conductivity artifacts

Correct Answer: Precipitation of stain causing granular deposits that may obscure structures

Q50. For quantitative particle size measurement from TEM micrographs, what step is essential to ensure accuracy?

• Using any magnification without calibration
• Calibrating magnification with a scale or standard and analyzing sufficient number of particles
• Relying solely on visual estimation
• Measuring only the largest particles

Correct Answer: Calibrating magnification with a scale or standard and analyzing sufficient number of particles

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com