Discussion
Assertion (A) : In most of commercial spectrophotometer lamp as source is preferred over laser as source.
Reason (R) : Laser as source is used only while using very small sample amount or volume as in case of coupling with separation technique.
Answer: C
The key reads both (A) and (R) are correct but (R) is not the correct explanation of (A).
The Assertion is true: commercial spectrophotometers use lamps such as tungsten-halogen and deuterium, which are cheap, stable and give a continuous range of wavelengths that a monochromator can scan. A laser gives only one or a few fixed lines.
The Reason is also accepted: lasers are used where a very intense, narrow beam has to be focused into a tiny volume, as in detectors coupled to capillary electrophoresis or micro-column separations. But that does not explain why lamps are preferred; the preference comes from cost and the need for a continuous spectrum. So the options calling either statement wrong do not fit.
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