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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 · 2025 · Paper I

Q2(d). Stoichiometry of NaCl doped with Ca²⁺

Question

In a sample of NaCl, one of every 10,000 sites, normally occupied by Na⁺, is occupied instead by Ca²⁺. Assuming that all of the Cl⁻ sites are fully occupied, what is the stoichiometry of the sample?

Answer in brief

Na₀.₉₉₉₈Ca₀.₀₀₀₁Cl.

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Topic notes: defects, non-stoichiometry and semiconductors, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversimpurity defectcation vacancySchottky defectaliovalent dopingnon-stoichiometryNaCl doped with CaCl2

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