CBSE Class 10 Answered

Dear Student

 Unsaturated hydrocarbons such as alkenes and alkynes are much more reactive than the parent alkanes. They react rapidly with bromine, for example, to add a Br₂ molecule across the C=C double bond.

This reaction provides a way to test for alkenes or alkynes. Solutions of bromine in CCl₄ have an intense red-orange color. When Br₂ in CCl₄ is mixed with a sample of an alkane, no change is initially observed. When it is mixed with an alkene or alkyne, the color of Br₂ rapidly disappears.

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