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Question

What sort of flame is produced when unsaturated carbon compounds are burnt in air?

This question was previously asked in
RRB Group D 2025 Question Paper (18-Aug-2026) (Shift 1)
The correct answer is

a yellow flame with lots of black smoke

Unsaturated carbon compounds (alkenes and alkynes) have double or triple bonds between carbon atoms and hence a higher proportion of carbon compared with saturated hydrocarbons. When they are burnt in air, the oxygen supply is usually not enough to burn all this carbon completely.

Because of this incomplete combustion, part of the carbon separates out as fine soot particles, giving the flame a bright yellow, luminous appearance along with a large amount of black smoke. Saturated hydrocarbons, in contrast, tend to burn with a clean blue flame in a good supply of air.

Hence, the answer is a yellow flame with lots of black smoke.

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Similar Questions

  1. What do methane, ethane and propane represent in the study of carbon compounds?

  2. Which property is most affected if the length of the carbon chain in an alkane increases?

  3. Which among the following molecular formulae of organic compounds does NOT represent a ring structure?

  4. Why do higher homologues of alkanes produce multiple products when they react with chlorine in a substitution reaction?

  5. Select the correct option regarding the following two statements labelled Assertion (A) and Reason (R).

    Assertion (A): Unsaturated hydrocarbons give a yellow flame with black smoke.

    Reason (R): They burn completely when oxygen is insufficient.

  6. Unsaturated hydrocarbons usually undergo which of the following reaction mechanisms?

  7. Which of the following statements about a homologous series are CORRECT?

    (1) All members have the same general formula.

    (2) Each successive member differs by a \(-CH_2-\) group.

    (3) Physical properties remain identical for all members.

  8. Which of the following hydrocarbons undergo addition reactions with hydrogen?

  9. A compound has the molecular formula C4H10. Which statement best describes its structure?

  10. Which of the following is NOT a characteristic of substitution reactions in alkanes?


Important Questions from Hydrocarbons

  1. Which of the following base is found in soap?

  2. Which one of the following is the general formula of Alkenes?

  3. \({\rm{C}}{{\rm{H}}_3}{\rm{COOH}}\mathop \to \limits^{LiAI{H_4}} {\rm{A}}\mathop \to \limits^{PC{I_5}} {\rm{B}}\mathop \to \limits^{alc.KOH} {\rm{C}}\) Homologue of ‘C’ in the above reaction is:
  4. Maximum quantity of carbon is present in

  5. Which of the following pair gives 1° carbonium ion by hydrolysis of C-Br bond?

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