Raman Spectroscopy: principle and applications MCQs With Answer

Raman Spectroscopy: principle and applications MCQs With Answer

This concise MCQ collection is designed for M.Pharm students preparing for MPC 201T Advanced Spectral Analysis. It focuses on the fundamentals and practical uses of Raman spectroscopy: the inelastic scattering principle, instrumentation components, selection rules, types of Raman techniques (resonance, SERS, TERS, CARS, FT‑Raman), and strategies to handle common problems such as fluorescence. Emphasis is placed on pharmaceutical applications like polymorph identification, API characterization, process analytical technology (PAT) and quantitative analysis with chemometrics. Each question is framed to test conceptual understanding and application in real pharmaceutical laboratory scenarios, with clear answers to aid efficient revision and exam readiness.

Q1. What fundamental molecular property change gives rise to Raman scattering?

• Change in dipole moment during vibration
• Change in polarizability during vibration
• Change in refractive index of the solvent
• Absorption of photon energy leading to fluorescence

Correct Answer: Change in polarizability during vibration

Q2. Which statement correctly contrasts Raman and infrared (IR) activity for molecular vibrations?

• Raman activity requires a change in dipole moment; IR requires a change in polarizability
• Raman and IR are identical; every vibration is active in both techniques
• Raman activity requires a change in polarizability; IR activity requires a change in dipole moment
• Raman detects only electronic transitions while IR detects vibrational transitions

Correct Answer: Raman activity requires a change in polarizability; IR activity requires a change in dipole moment

Q3. Why are Stokes Raman lines generally more intense than anti‑Stokes lines at room temperature?

• Because Stokes scattering originates from excited vibrational states which are more populated
• Because Stokes photons have higher energy than incident photons
• Because most molecules are in the vibrational ground state, making Stokes transitions more probable
• Because anti‑Stokes lines are absorbed by the sample

Correct Answer: Because most molecules are in the vibrational ground state, making Stokes transitions more probable

Q4. In which units is the Raman shift most commonly reported?

• Nanometers (nm)
• Electronvolts (eV)
• Wavenumbers (cm⁻¹)
• Hertz (Hz)

Correct Answer: Wavenumbers (cm⁻¹)

Q5. Which mathematical property of the polarizability tensor determines Raman activity of a normal mode?

• Magnitude of the dipole derivative
• Non‑zero derivative of polarizability with respect to the vibrational coordinate
• Absolute polarizability value at equilibrium geometry
• Spin multiplicity of the electronic ground state

Correct Answer: Non‑zero derivative of polarizability with respect to the vibrational coordinate

Q6. What is the primary advantage of resonance Raman spectroscopy?

• It eliminates the need for monochromatic lasers
• It selectively enhances vibrations associated with an electronic chromophore when the excitation coincides with an electronic transition
• It suppresses fluorescence completely for all samples
• It measures only lattice vibrations in solids

Correct Answer: It selectively enhances vibrations associated with an electronic chromophore when the excitation coincides with an electronic transition

Q7. Surface‑enhanced Raman scattering (SERS) enhancement is primarily due to which mechanisms?

• Only an increase in sample temperature near the metal surface
• Electromagnetic enhancement from localized surface plasmons and chemical (charge‑transfer) enhancement
• Simple concentration of analyte molecules with no optical effects
• Resonant absorption by the metal nanoparticles causing new vibrational modes

Correct Answer: Electromagnetic enhancement from localized surface plasmons and chemical (charge‑transfer) enhancement

Q8. Why is 1064 nm excitation commonly used in FT‑Raman instruments for pharmaceutical samples?

• Because 1064 nm gives the highest Raman scattering cross‑section for all bonds
• Because 1064 nm excitation increases fluorescence in organic compounds
• Because 1064 nm (NIR) reduces sample fluorescence and minimizes photodegradation for many pharmaceutical samples
• Because detectors cannot record visible Raman signals

Correct Answer: Because 1064 nm (NIR) reduces sample fluorescence and minimizes photodegradation for many pharmaceutical samples

Q9. Which detector is most commonly used in dispersive (grating) Raman spectrometers for visible excitation?

• Photomultiplier tube (PMT) designed for UV only
• Liquid‑nitrogen cooled bolometer
• Charge‑coupled device (CCD) detector
• Thermocouple detector

Correct Answer: Charge‑coupled device (CCD) detector

Q10. Which optical component is typically used to remove the intense Rayleigh (elastic) scattered light and allow detection of Raman lines close to the laser line?

• Band‑pass filter that transmits only the laser wavelength
• Notch or edge filter that rejects the laser line while transmitting Stokes/anti‑Stokes bands
• Polarizer that blocks all scattered light
• Interference heater to shift the laser frequency

Correct Answer: Notch or edge filter that rejects the laser line while transmitting Stokes/anti‑Stokes bands

Q11. Which statement best describes coherent anti‑Stokes Raman scattering (CARS)?

• CARS is a linear spontaneous scattering process yielding Stokes lines only
• CARS is a nonlinear, coherent technique producing an enhanced anti‑Stokes signal using multiple synchronized laser beams
• CARS eliminates the need for laser sources by using thermal emission
• CARS measures only fluorescence lifetimes

Correct Answer: CARS is a nonlinear, coherent technique producing an enhanced anti‑Stokes signal using multiple synchronized laser beams

Q12. Compared with fluorescence, Raman scattering cross‑sections are generally:

• Much larger, making Raman always more sensitive than fluorescence
• Much smaller, so Raman signals are typically weaker than fluorescence emissions
• Identical for all chromophores
• Independent of excitation wavelength

Correct Answer: Much smaller, so Raman signals are typically weaker than fluorescence emissions

Q13. What does a low depolarization ratio (I⊥/I∥ significantly less than 0.75) indicate for a Raman band?

• The band arises from an antisymmetric stretch and is non‑Raman active
• The band corresponds to a totally symmetric vibration and is polarized
• The band is contaminated by fluorescence and should be ignored
• The instrument alignment is incorrect

Correct Answer: The band corresponds to a totally symmetric vibration and is polarized

Q14. Which of the following is a primary pharmaceutical application of Raman spectroscopy?

• Measurement of drug pKa by potentiometry
• Polymorph identification and solid‑state form characterization of active pharmaceutical ingredients (APIs)
• Determination of bioavailability using dissolution alone
• Measurement of microbial contamination by colony counting

Correct Answer: Polymorph identification and solid‑state form characterization of active pharmaceutical ingredients (APIs)

Q15. What is an effective strategy to minimize fluorescence interference during Raman analysis of organic pharmaceuticals?

• Switch to shorter wavelength UV excitation to quench fluorescence
• Use near‑infrared (NIR) excitation (e.g., 785 or 1064 nm) or time‑gated detection to reduce fluorescence background
• Always dilute the sample in water to remove fluorescence
• Increase laser power indefinitely until fluorescence disappears

Correct Answer: Use near‑infrared (NIR) excitation (e.g., 785 or 1064 nm) or time‑gated detection to reduce fluorescence background

Q16. For quantitative analysis using Raman spectroscopy, which statement is most accurate?

• Raman intensity is unrelated to concentration, so quantitation is impossible
• Raman peak intensity is theoretically proportional to concentration but requires calibration, accounting for matrix effects and instrument response
• Single raw spectrum without calibration always yields absolute concentrations
• Only peak positions, not intensities, are useful for quantitation

Correct Answer: Raman peak intensity is theoretically proportional to concentration but requires calibration, accounting for matrix effects and instrument response

Q17. What advantage does confocal Raman microscopy provide for pharmaceutical solid samples?

• It simplifies spectra by averaging bulk and surface signals only
• It allows spatially resolved chemical mapping and depth profiling with micrometer lateral and sub‑micrometer axial resolution
• It eliminates the need for a laser source
• It converts Raman spectra into IR spectra automatically

Correct Answer: It allows spatially resolved chemical mapping and depth profiling with micrometer lateral and sub‑micrometer axial resolution

Q18. How does the Raman shift (in cm⁻¹) behave when the excitation laser wavelength is changed for the same vibrational mode?

• The Raman shift in cm⁻¹ changes unpredictably with laser wavelength
• The Raman shift in cm⁻¹ remains essentially the same for the same vibrational mode, independent of excitation wavelength
• The Raman shift always doubles if the wavelength is halved
• Raman shift becomes negative when using longer wavelengths

Correct Answer: The Raman shift in cm⁻¹ remains essentially the same for the same vibrational mode, independent of excitation wavelength

Q19. Tip‑enhanced Raman spectroscopy (TERS) is most appropriately described as:

• A far‑field technique using large aperture lenses for bulk analysis
• A near‑field technique that uses a metalized AFM/STM tip to enhance and spatially confine Raman signals at the nanoscale
• A fluorescence technique that enhances emission via quantum dots
• An FT‑IR method combined with Raman detectors

Correct Answer: A near‑field technique that uses a metalized AFM/STM tip to enhance and spatially confine Raman signals at the nanoscale

Q20. Which safety practice is essential when operating Raman instruments with laser excitation in a pharmaceutical laboratory?

• No special precautions are needed because Raman lasers are harmless
• Use appropriate laser eye protection, beam enclosures, interlocks and training to prevent eye and skin exposure
• Only wear gloves; eye protection is unnecessary
• Operate the laser at maximum power in crowded spaces to speed up acquisition

Correct Answer: Use appropriate laser eye protection, beam enclosures, interlocks and training to prevent eye and skin exposure

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