Understanding the principles of interaction between matter and electromagnetic radiation is essential for B. Pharm students preparing for analytical and spectroscopic applications. This concise guide covers core concepts—absorption, emission, scattering, electronic and vibrational transitions, Beer–Lambert law, molar absorptivity, selection rules, and photophysical processes—used in UV‑Vis, IR, NMR, Raman and fluorescence spectroscopy. Emphasis on instrumentation, sample factors, spectral interpretation and common deviations builds practical insight for drug analysis, stability testing and formulation work. Keywords: interaction of matter and electromagnetic radiation, spectroscopy, Beer‑Lambert law, molar absorptivity, UV‑Vis, IR, NMR, fluorescence, Raman, photochemistry. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which mathematical expression represents the Beer–Lambert law relating absorbance to concentration?
- A = ε × l × c
- A = I0 / I
- A = log10(I / I0)
- A = λ × ν
Correct Answer: A = ε × l × c
Q2. Which relation correctly links photon energy (E) and wavelength (λ)?
- E = k × T
- E = hc / λ
- E = λ / c
- E = m × c^2
Correct Answer: E = hc / λ
Q3. Which spectral region is most informative for identifying functional groups via vibrational transitions?
- Infrared (IR) spectroscopy
- Microwave spectroscopy
- Gamma-ray spectroscopy
- UV-Visible spectroscopy
Correct Answer: Infrared (IR) spectroscopy
Q4. UV‑Vis spectroscopy primarily probes which type of molecular transition?
- Electronic transitions (π→π*, n→π*)
- Nuclear spin transitions
- Rotational transitions only
- Core electron ionization
Correct Answer: Electronic transitions (π→π*, n→π*)
Q5. What molecular change must occur for a vibration to be IR active?
- Change in molecular dipole moment during vibration
- Change in molecular polarizability only
- Rotation about a single bond
- Emission of a photon without dipole change
Correct Answer: Change in molecular dipole moment during vibration
Q6. Which instrument component separates wavelengths in a spectrophotometer?
- Monochromator (diffraction grating or prism)
- Ionization chamber
- Fourier transform mirror only
- Mass analyzer
Correct Answer: Monochromator (diffraction grating or prism)
Q7. Which factor most strongly affects the position of an IR absorption band?
- Bond force constant and reduced mass
- Number of isotopes only
- Sample pH exclusively
- Magnetic field strength
Correct Answer: Bond force constant and reduced mass
Q8. What are the units of molar absorptivity (ε)?
- L·mol^-1·cm^-1
- W·m^-2
- ppm
- mol·L^-1
Correct Answer: L·mol^-1·cm^-1
Q9. Which condition commonly causes deviation from the Beer–Lambert law?
- High analyte concentration causing aggregation or chemical association
- Using a 1 cm cuvette at low concentration
- Measuring at peak absorbance with dilute solution
- Using monochromatic light within linear range
Correct Answer: High analyte concentration causing aggregation or chemical association
Q10. How do fluorescence and phosphorescence primarily differ?
- Fluorescence: singlet→singlet short-lived; phosphorescence: triplet→singlet longer-lived
- Fluorescence arises from triplet states only
- Phosphorescence is instantaneous emission
- Fluorescence requires ionization
Correct Answer: Fluorescence: singlet→singlet short-lived; phosphorescence: triplet→singlet longer-lived
Q11. What does a Jablonski diagram illustrate?
- Electronic states, vibrational levels, and radiative/nonradiative transitions
- Mass-to-charge fragmentation pathways
- Chromatographic retention mechanisms
- NMR spin–spin coupling patterns
Correct Answer: Electronic states, vibrational levels, and radiative/nonradiative transitions
Q12. Quantum yield of fluorescence is defined as:
- Number of photons emitted divided by number of photons absorbed
- Ratio of emission wavelength to absorption wavelength
- Lifetime of excited state in seconds
- Energy gap between HOMO and LUMO
Correct Answer: Number of photons emitted divided by number of photons absorbed
Q13. Raman spectroscopy primarily provides information about:
- Vibrational modes via inelastic scattering of light
- Nuclear spin transitions in a magnetic field
- Core electron binding energies
- Purely electronic excited states without vibrational detail
Correct Answer: Vibrational modes via inelastic scattering of light
Q14. One major advantage of FT‑IR over dispersive IR is:
- Multiplex and throughput advantages leading to better S/N and faster scans
- Lower initial instrument cost always
- Complete elimination of water interference
- Direct measurement of electronic transitions
Correct Answer: Multiplex and throughput advantages leading to better S/N and faster scans
Q15. In NMR spectroscopy, chemical shift is reported relative to which reference and in what units?
- Relative to TMS in parts per million (ppm)
- Relative to water in Hertz (Hz)
- Relative to benzene in percent (%)
- Absolute frequency in gigahertz (GHz)
Correct Answer: Relative to TMS in parts per million (ppm)
Q16. What information does spin–spin coupling in 1H NMR provide?
- Number and proximity of neighboring magnetic nuclei (coupling constants and splitting)
- Molecular weight directly
- Vibrational frequencies of bonds
- Absolute concentration without reference
Correct Answer: Number and proximity of neighboring magnetic nuclei (coupling constants and splitting)
Q17. Which nucleus is most sensitive in NMR for routine pharmaceutical analysis?
- Proton (1H) NMR
- Carbon‑13 (13C) NMR exclusively
- Nitrogen‑15 (15N) for all drugs
- Fluorine‑19 always preferred
Correct Answer: Proton (1H) NMR
Q18. Which mass spectrometry ionization technique is best for thermally labile, polar pharmaceutical molecules?
- Electrospray ionization (ESI)
- Electron ionization (EI)
- Fast atom bombardment (FAB) only
- Flame ionization
Correct Answer: Electrospray ionization (ESI)
Q19. A bathochromic (red) shift in UV‑Vis spectra is most commonly caused by:
- Increased conjugation or greater solvent polarity/polarizability
- Decreased conjugation and higher energy transitions
- Instrumental baseline drift only
- Lowering path length in the cuvette
Correct Answer: Increased conjugation or greater solvent polarity/polarizability
Q20. A very high molar absorptivity (ε) at an absorption maximum indicates:
- Strong absorption and high analytical sensitivity at that wavelength
- Very low probability of electronic transition
- No practical use for quantitative work
- Instrumental malfunction
Correct Answer: Strong absorption and high analytical sensitivity at that wavelength
Q21. Transmittance (T) in spectrophotometry is defined as:
- Transmitted intensity divided by incident intensity (I / I0)
- Logarithm of absorbance
- Absorbance multiplied by path length
- Difference between I0 and I in moles
Correct Answer: Transmitted intensity divided by incident intensity (I / I0)
Q22. Which technique is most complementary to IR for vibrational information and less sensitive to water?
- Raman spectroscopy
- UV‑Vis spectroscopy
- NMR spectroscopy
- Gas chromatography
Correct Answer: Raman spectroscopy
Q23. What does photobleaching refer to in fluorescence studies?
- Irreversible loss of fluorescence due to photochemical decomposition
- Temporary quenching that recovers in seconds
- Increase in fluorescence intensity over time
- Complete conversion of photons into heat only
Correct Answer: Irreversible loss of fluorescence due to photochemical decomposition
Q24. What is Stokes shift?
- Difference where emission occurs at longer wavelength than absorption
- Shift of absorption to shorter wavelength only
- Change in mass-to-charge ratio in MS
- Difference in chemical shift between two NMR peaks
Correct Answer: Difference where emission occurs at longer wavelength than absorption
Q25. In UV‑Vis spectrophotometry, how does path length (l) affect absorbance?
- Absorbance increases linearly with path length (A ∝ l)
- Absorbance decreases exponentially with path length
- Absorbance is independent of path length
- Path length only affects fluorescence, not absorbance
Correct Answer: Absorbance increases linearly with path length (A ∝ l)
Q26. Which detector is typically most sensitive for low light levels in UV‑Vis instruments?
- Photomultiplier tube (PMT)
- Thermocouple detector
- Electron multiplier for IR only
- Ordinary silicon webcam
Correct Answer: Photomultiplier tube (PMT)
Q27. NMR resonance occurs when:
- Radiofrequency matches the energy difference between nuclear spin states in a magnetic field
- UV light excites electrons to higher orbitals
- Sample is heated to boiling point
- Electrons are ejected by high‑energy photons
Correct Answer: Radiofrequency matches the energy difference between nuclear spin states in a magnetic field
Q28. Which solvent effect can alter spectral band positions in UV‑Vis and fluorescence?
- Polarity and hydrogen‑bonding interactions with the solute
- Only the solvent’s boiling point
- Color of the container
- Magnetic susceptibility exclusively
Correct Answer: Polarity and hydrogen‑bonding interactions with the solute
Q29. Which spectroscopic technique is most commonly used for routine quantitative assay of drugs in formulations?
- UV‑Visible spectrophotometry
- Raman imaging only
- NMR for all routine tablet assays
- Atomic absorption spectroscopy for organics
Correct Answer: UV‑Visible spectrophotometry
Q30. Which is an example of a photochemical reaction relevant to pharmaceutical compounds?
- Cis–trans isomerization of a drug molecule upon light exposure
- Simple evaporation of solvent
- pH‑dependent protonation in the dark only
- Chromatographic separation under UV detection
Correct Answer: Cis–trans isomerization of a drug molecule upon light exposure
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.
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