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NEET-UG Biology

Detection of extra elements — practice questions

4 questions in the bank on this idea. Below are 4 of them, exactly as they appear in a test.

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  1. Question 1 · difficulty L2 · understanding

    Why is an organic compound fused with sodium before testing for nitrogen, sulphur or halogens?

    • A. It forms water-soluble ionic sodium salts of the extra elements
    • B. Fusion removes carbon completely before the test
    • C. Sodium acts only as an indicator for the final colour
    • D. Fusion converts every heteroatom directly into its free element

  2. Question 2 · difficulty L3 · application

    A sodium extract gives a Prussian-blue colour after the appropriate iron treatment. Which extra element is indicated?

    • A. Sulphur
    • B. Nitrogen
    • C. Chlorine
    • D. Phosphorus

  3. Question 3 · difficulty L3 · application

    An organic compound containing both nitrogen and sulphur gives a blood-red colour with ferric ions after sodium fusion. Which species is responsible?

    • A. Chloride ion
    • B. Cyanide ion
    • C. Sulphate ion (SO4^2−)
    • D. Thiocyanate ion

  4. Question 4 · difficulty L4 · analysis

    Before adding silver nitrate in the halogen test, why is the sodium extract boiled with nitric acid?

    • A. It reduces silver ions so that metallic silver is produced
    • B. It supplies chloride ions needed to form the precipitate
    • C. It removes interfering cyanide and sulphide ions
    • D. It converts all halides into volatile hydrogen halides

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