The reagent used to distinguish an alkene from an alkane in the laboratory is

  • A. sodium metal
  • B. silver nitrate solution
  • C. bromine water, which is decolourised by the alkene
  • D. limewater

Explanation

The orange colour of bromine water disappears as bromine adds across the double bond to form a colourless dibromo compound, and an alkane leaves the colour unchanged in the dark. Acidified potassium permanganate, which loses its purple colour, is the other standard test. Silver nitrate is used to test for halide ions and limewater for carbon dioxide.

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