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UPSC Combined Geo-Scientist

Chemist

  • 3 descriptive papers
  • 200 marks each
  • 3 h per paper

Mains Paper II covers physical chemistry.

UPSC Combined Geo-Scientist, Mains · 2022 · Mains Paper II

Q3. Compactness of simple cubic, bcc and fcc crystals

Question

Establish the relative order of compactness between simple cubic, body centered cubic and face centered cubic crystals. Draw diagrams, if needed.

Answer in brief

Packing fraction: fcc 0.740 (74.0 %) > bcc 0.680 (68.0 %) > sc 0.524 (52.4 %); compactness: fcc > bcc > sc.

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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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Read the whole 2022 solution2022 question paper

Topic notes: crystal systems, Bragg's law, X-ray diffraction and radius ratio, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverspacking fractionsimple cubicbody-centred cubicface-centred cubiccoordination numberunit cell