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Indian Forest Service (Mains)

Chemistry optional

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

Paper I covers physical and inorganic chemistry.

Indian Forest Service (Mains), Chemistry optional · 2022 · Paper I

Q2(c)(i). Limiting radius ratio for trigonal coordination

Question

Prove that the minimum value of RA/RX = 0.155 will provide a 3:3 coordination for A and X ions in an AX compound (A is the cation, X is the anion, RA is the radius of the cation, RX is the radius of the anion).

Answer in brief

For a cation in a triangular hole, (RA/RX)min = 2/√3 − 1 = 0.1547 ≈ 0.155.

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

Coversradius ratiolimiting radius ratio 0.155trigonal coordinationtriangular voidionic crystal geometry

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