Q.39 Which of the following statements is/are CORRECT?
(A) Absorption occurs at all wavelengths if light passes through a given solution.
(B) The efficiency of a photochemical process is often expressed in terms of quantum yield.
(C) The unit of molar extinction coefficient is litre mole-1 cm.
(D) The extent of absorption in a dilute solution would be the same if the concentration is
doubled and the path-length of light passing through solution is halved.
Correct statements are (B), (C), and (D).
Option Analysis
(A) Incorrect
Absorption does not occur uniformly across all wavelengths; molecules absorb specifically at wavelengths matching electronic transitions, producing characteristic spectra. Transparent regions exist where no absorption happens.
(B) Correct
Quantum yield (Φ) quantifies photochemical efficiency as molecules reacted (or products formed) per photon absorbed, essential for processes like photosynthesis or photodissociation.
(C) Correct
Molar extinction coefficient (ε) from Beer-Lambert law A=εcl has units L mol⁻¹ cm⁻¹, balancing absorbance (unitless), concentration (mol L⁻¹), and path length (cm).
(D) Correct
Beer-Lambert law states absorbance depends on c×l product. Doubling concentration (2c) and halving path length (l/2) keeps c×l constant, so absorption remains unchanged.
Molar extinction coefficient Beer-Lambert law quantum yield absorption concepts form core photochemistry topics for CSIR NET Life Sciences. This MCQ tests understanding of spectroscopic principles crucial for UV-Vis analysis in biochemistry and molecular biology exams.
Core Principles
Beer-Lambert law A=εcl governs light absorption, where ε (molar extinction coefficient) quantifies absorption strength at specific wavelengths. Quantum yield measures photochemical reaction efficiency.
Exam Relevance
CSIR NET frequently assesses these via numericals on path length/concentration changes and conceptual errors like uniform absorption. Dilute solutions maintain proportional absorbance.
