In unsaturated hydrocarbons, electrons favor ?

Unsaturated hydrocarbons include alkenes (C=C) and alkynes (C≡C) — compounds containing one or more multiple carbon–carbon bonds. These bonds consist of a sigma (σ) bond and one or more pi (π) bonds. The π-electrons are loosely held and exist above and below the plane of the molecule, making them easily available for chemical attack by electrophiles (electron-seeking species).

This availability of π-electrons makes unsaturated hydrocarbons more reactive than saturated hydrocarbons (alkanes). The characteristic type of reaction they undergo is addition reaction, where atoms or groups of atoms add across the double or triple bond, converting the molecule into a more saturated compound.

For example:
Ethene addition reaction with hydrogen (hydrogenation):
CH₂=CH₂ + H₂ → CH₃–CH₃

Addition of halogens:
CH₂=CH₂ + Br₂ → CH₂Br–CH₂Br

Addition of hydrogen halides:
CH₂=CH₂ + HCl → CH₃–CH₂Cl

These reactions occur because the π-bond is weaker than the σ-bond and breaks easily under mild conditions. The addition of atoms or groups converts the double or triple bond into a single bond, thereby increasing the compound’s stability.

Key Points:

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  Unsaturated hydrocarbons: Alkenes (C=C) and Alkynes (C≡C).

  
  


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  Reactive part: π-bond electrons.

  
  


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  Reaction type: Addition reactions (hydrogenation, halogenation, hydrohalogenation, hydration).

  
  


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  Reason: π-electrons are exposed and readily attract electrophiles.

  
  


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  Result: The compound becomes more saturated and stable.

  
  

Hence, in unsaturated hydrocarbons, the electrons favor addition reactions due to their high reactivity and electron density around the multiple bonds.

✅ Correct Option: B) Addition reactions