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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 · 2021 · Paper I

Q2(a). Hydrogen atom: the transition n = 101 → 100

Question

Hydrogen atoms are observed to have radiative transitions from n = 101 to n = 100 to occur. (i) What are the frequency and wavelength of the radiation emitted in this transition? (ii) Why is it difficult to observe this transition?

Answer in brief

(i) ν = 6.48 × 10⁹ Hz (6.48 GHz) and λ = 4.63 cm, in the microwave region; (ii) the line is very weak, and so large an atom is easily ionised.

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Topic notes: the hydrogen atom: Schrödinger equation in spherical coordinates, quantum numbers, radial distribution, nodes and orbital shapes, with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversRydberg formulaRydberg atomhydrogen spectrummicrowave transitioncorrespondence principle

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