Hydrocarbons Quiz - CBSE Class 12 Chemistry

Free practice quiz: Hydrocarbons (CBSE Class 12 Chemistry). 14 multiple-choice questions with answers and explanations. Play online, no sign-up needed.

Sample questions

1. Which of the following is NOT a hydrocarbon?

   1. Ethane
   2. Benzene
   3. Ethanol
   4. Propene
   Show answer

   Answer: C. Ethanol

   Ethanol contains an -OH hydroxyl group, making it an alcohol, not a hydrocarbon. Hydrocarbons contain only carbon and hydrogen atoms.

2. Which type of hybridization is present in ethene?

   1. sp
   2. sp²
   3. sp³
   4. dsp²
   Show answer

   Answer: B. sp²

   Ethene (C₂H₄) has a double bond between the carbon atoms, requiring sp² hybridization to form three sigma bonds and one pi bond.

3. Describe the process of cracking and its importance in the petroleum industry.

   1. Cracking is the process of breaking down large hydrocarbon molecules into smaller, more useful ones. It's important for producing gasoline and other fuels.
   2. Cracking is the process of combining small hydrocarbon molecules into larger ones. It's important for producing lubricants.
   3. Cracking is the process of purifying hydrocarbons. It's important for removing impurities.
   4. Cracking is the process of separating hydrocarbons based on their boiling points. It's important for refining petroleum.
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   Answer: A. Cracking is the process of breaking down large hydrocarbon molecules into smaller, more useful ones. It's important for producing gasoline and other fuels.

   Cracking converts long-chain alkanes into shorter, branched-chain alkanes and alkenes, which are more valuable as fuels.

4. Discuss the concept of resonance in conjugated dienes and its effect on stability.

   1. Resonance in conjugated dienes leads to increased stability due to delocalization of pi electrons.
   2. Resonance in conjugated dienes leads to decreased stability due to increased electron repulsion.
   3. Resonance has no effect on the stability of conjugated dienes.
   4. Resonance in conjugated dienes leads to increased reactivity.
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   Answer: A. Resonance in conjugated dienes leads to increased stability due to delocalization of pi electrons.

   Delocalization of pi electrons through resonance lowers the overall energy of the molecule, increasing its stability.

5. Explain the concept of aromaticity and give examples of aromatic hydrocarbons.

   1. Aromaticity refers to the stability of cyclic, planar molecules with a delocalized pi electron system following Huckel's rule (4n+2 pi electrons). Examples include benzene and naphthalene.
   2. Aromaticity refers to the reactivity of cyclic, planar molecules. Examples include cyclohexane and cyclopentane.
   3. Aromaticity is a property of all cyclic compounds.
   4. Aromaticity refers to the instability of cyclic, planar molecules.
   Show answer

   Answer: A. Aromaticity refers to the stability of cyclic, planar molecules with a delocalized pi electron system following Huckel's rule (4n+2 pi electrons). Examples include benzene and naphthalene.

   Aromaticity is a special stability conferred by a delocalized pi electron cloud satisfying specific structural requirements.

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