Class 9 Chemistry MCQs: Hydrocarbons

MCQs (sample)

Showing 25 questions from this chapter. For a full timed test, use “Start online test”.

1. 1. What is the nature of alkane molecules?

   • Non-polar
   • Polar
   • Ionic
   • Highly reactive
   Answer & explanation

   Correct: Non-polar

   Alkane molecules are essentially non-polar.

2. 2. What is hydrogenation in the context of alkanes?

   • Addition of hydrogen across carbon-carbon multiple bonds
   • Breaking down larger hydrocarbons
   • Reduction of alkyl halides
   • Formation of alkenes from alkanes
   Answer & explanation

   Correct: Addition of hydrogen across carbon-carbon multiple bonds

   Hydrogenation refers to the addition of hydrogen molecules across carbon-carbon multiple bonds.

3. 3. What are hydrocarbons primarily composed of?

   • Carbon and hydrogen
   • Oxygen and hydrogen
   • Nitrogen and carbon
   • Sulfur and hydrogen
   Answer & explanation

   Correct: Carbon and hydrogen

   Hydrocarbons are defined as organic compounds that contain only two elements: carbon and hydrogen.

4. 4. How do alkanes typically behave in water?

   • Dissolve in water
   • Float on water
   • Less dense than water and do not dissolve
   • React with water
   Answer & explanation

   Correct: Less dense than water and do not dissolve

   Alkanes are less dense than water and do not dissolve in it.

5. 5. At what temperature does hydrogenation typically occur when using finely divided nickel?

   • 200-300°C
   • 150-200°C
   • 300-350°C
   • 400-450°C
   Answer & explanation

   Correct: 200-300°C

   Hydrogenation occurs at temperatures between 200-300°C in the presence of finely divided nickel.

6. 6. What is the general formula for alkanes?

   • CnH2n+2
   • CnH2n
   • C2nH2n+1
   • C3nH2n-2
   Answer & explanation

   Correct: CnH2n+2

   The general formula for alkanes is CnH2n+2 where n represents the number of carbon atoms.

7. 7. What type of reaction occurs between alkanes and halogens in sunlight?

   • Reduction reaction
   • Decomposition reaction
   • Photochemical substitution reaction
   • Complete combustion reaction
   Answer & explanation

   Correct: Photochemical substitution reaction

   A chemical reaction that occurs in sunlight is called a photochemical reaction, and it is a substitution reaction.

8. 8. What is released when zinc reacts with an aqueous acid during the reduction of alkyl halides?

   • Nascent hydrogen
   • Carbon dioxide
   • Hydrogen chloride
   • Oxygen
   Answer & explanation

   Correct: Nascent hydrogen

   Zinc liberates atomic hydrogen, known as nascent hydrogen, when it reacts with an aqueous acid.

9. 9. Which of the following is the simplest alkane?

   • Methane
   • Ethane
   • Propane
   • Butane
   Answer & explanation

   Correct: Methane

   Methane (CH4) is the simplest alkane molecule.

10. 10. What are the products of the complete combustion of methane?

    • Carbon monoxide and water
    • Carbon dioxide, water, and heat
    • Carbon, hydrogen, and heat
    • Halogen and water
    Answer & explanation

    Correct: Carbon dioxide, water, and heat

    Complete combustion of an alkane produces carbon dioxide, water, and heat.

11. 11. Which reaction results in the production of ethane from ethene?

    • CH2=CH2 + H2 -> CH3-CH3
    • C10H22 -> C8H18 + C2H4
    • CH3-Cl + 2[H] -> CH4
    • CH≡CH + H2 -> CH2=CH2
    Answer & explanation

    Correct: CH2=CH2 + H2 -> CH3-CH3

    The reaction CH2=CH2 + H2 -> CH3-CH3 is the hydrogenation of ethene to produce ethane.

12. 12. How many hydrogen atoms are in ethane (C2H6)?

    • 4
    • 6
    • 2
    • 8
    Answer & explanation

    Correct: 6

    Ethane, with the formula C2H6, contains 6 hydrogen atoms.

13. 13. Which alkanes are colorless and odorless gases?

    • Alkanes with more than four carbon atoms
    • Alkanes containing up to four carbon atoms
    • All alkanes
    • Only solid alkanes
    Answer & explanation

    Correct: Alkanes containing up to four carbon atoms

    Alkanes containing up to four carbon atoms are colorless and odorless gases.

14. 14. What type of reaction is involved in the reduction of alkyl halides?

    • Oxidation
    • Hydrolysis
    • Reduction
    • Decomposition
    Answer & explanation

    Correct: Reduction

    The reduction of alkyl halides involves adding nascent hydrogen, which is a reduction process.

15. 15. What type of hydrocarbons are alkanes classified as?

    • Saturated hydrocarbons
    • Unsaturated hydrocarbons
    • Aromatic hydrocarbons
    • Cyclic hydrocarbons
    Answer & explanation

    Correct: Saturated hydrocarbons

    Alkanes are categorized as saturated hydrocarbons because they contain only single bonds between carbon atoms.

16. 16. What happens during the incomplete combustion of methane?

    • CO and C are produced
    • Only CO2 is produced
    • Only water is produced
    • No products are formed
    Answer & explanation

    Correct: CO and C are produced

    Incomplete combustion of methane gives carbon monoxide (CO), carbon (C), and water (H2O).

17. 17. What does thermal cracking produce when a large hydrocarbon is heated?

    • Singular alkanes only
    • A mixture of alkanes and alkenes
    • Only alkenes
    • Halides
    Answer & explanation

    Correct: A mixture of alkanes and alkenes

    Thermal cracking produces a mixture of alkanes and alkenes when large hydrocarbons are heated.

18. 18. What is the main component of natural gas?

    • Methane
    • Ethane
    • Propane
    • Butane
    Answer & explanation

    Correct: Methane

    Methane is the primary component of natural gas.

19. 19. Which of the following is a use of hexane?

    • As a fuel
    • To extract vegetable oils
    • To dissolve ionic compounds
    • As an explosive
    Answer & explanation

    Correct: To extract vegetable oils

    Hexane is used to extract vegetable oils from sources like corn and soybeans.

20. 20. In the hydrogenation of alkynes, how many molecules of hydrogen add to the molecule?

    • One
    • Two
    • Three
    • Four
    Answer & explanation

    Correct: Two

    Alkynes add two molecules of hydrogen during the hydrogenation process.

21. 21. When carbon atoms are connected by single bonds in a hydrocarbon, what type of hydrocarbon is it?

    • Alkane
    • Alkene
    • Alkyne
    • None of the above
    Answer & explanation

    Correct: Alkane

    Hydrocarbons with single bonds between carbon atoms are classified as alkanes.

22. 22. What type of flame do most alkanes burn with?

    • Yellow flame
    • Red flame
    • Blue flame
    • No flame
    Answer & explanation

    Correct: Blue flame

    Most alkanes burn with a blue flame.

23. 23. What is the purpose of adding zinc to alkyl halides?

    • To create alkenes
    • To produce nascent hydrogen
    • To heat the reaction
    • To increase pressure
    Answer & explanation

    Correct: To produce nascent hydrogen

    Zinc is added to alkyl halides to produce nascent hydrogen which facilitates their reduction.

24. 24. If n=1 in the alkane formula CnH2n+2, how many hydrogen atoms would there be?

    • 2
    • 4
    • 6
    • 8
    Answer & explanation

    Correct: 4

    Plugging n=1 into the formula gives C1H2(1)+2 which results in CH4, implying there are 4 hydrogen atoms.

25. 25. What effect does sunlight have on the reaction of methane with chlorine?

    • Makes it a complete reaction
    • Causes an explosion in direct sunlight
    • Produces energy immediately
    • Eliminates production of HCl
    Answer & explanation

    Correct: Causes an explosion in direct sunlight

    In direct sunlight, the reaction of methane with chlorine is explosive and forms carbon and HCl.