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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

Q2(c). Primitive cubic lattice: points, voids and the sphere at the centre

Question

Consider a primitive cubic lattice structure of an element. (i) How many lattice points are present in this unit cell? (ii) What is the coordination number of the atom present in this structure? (iii) What is the percentage void volume of this structure? (iv) If the radius of the atom present in this lattice is 178.1 pm, find the radius of the sphere that can fit in the centre of this cubic unit cell. (v) What is the coordination number of this sphere?

Answer in brief

(i) 1; (ii) 6; (iii) 47.6 %; (iv) r = (√3 − 1)R = 130.4 pm; (v) 8.

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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 →

Coverssimple cubic latticepacking fractioncubic voidradius ratiocoordination numberCsCl structure

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