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UPSC Civil Services (Mains)

Chemistry optional

  • 2 papers
  • 250 marks each
  • 3 h per paper
  • 5 of 8 questions, Q1 and Q5 compulsory

Paper I covers physical and inorganic chemistry.

UPSC Civil Services (Mains), Chemistry optional · 2023 · Paper I

Q8(c). Light absorbed when the path length is halved

Question

When incident light of wavelength 300 nm is passed through a solution in a 1 cm cell, it transmits only 10% of the incident light. What percentage of light would be absorbed by the same solution if taken in a 0.5 cm cell?

Answer in brief

68.4 % absorbed (31.6 % transmitted).

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The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

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Topic notes: photochemistry (quantum yield, Jablonski diagram, H₂–halogen reactions), with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversBeer–Lambert lawabsorbancetransmittancepath lengthmolar absorptivity

All parts of Question 8