King Edward Medical University Entry Test Chemistry: Hydrocarbons MCQs

King Edward Medical University Entry Test Chemistry: Hydrocarbons MCQs — sample questions

1. Question 1

   Q1. The reaction of methane with chlorine in the presence of sunlight is an example of which type of reaction?

   • A) Substitution reaction
   • B) Addition reaction
   • C) Elimination reaction
   • D) Polymerization reaction

   Answer: Substitution reaction

   Explanation: Methane reacts with chlorine through a substitution reaction, replacing H with Cl. Addition is incorrect as it involves unsaturated compounds.

2. Question 2

   Q2. Which alkene will produce 2-butanol upon hydration?

   • A) 1-Butene
   • B) 2-Butene
   • C) Isobutene
   • D) 1-Pentene

   Answer: 2-Butene

   Explanation: 2-Butene upon hydration gives 2-butanol. 1-Butene gives 2-butanol too, but it's not the only product.

3. Question 3

   Q3. The general formula for alkynes is

   • A) CnH2n+2
   • B) CnH2n
   • C) CnH2n-2
   • D) CnHn

   Answer: CnH2n-2

   Explanation: Alkynes have the general formula CnH2n-2 due to two hydrogen atoms being less than alkanes for each triple bond.

4. Question 4

   Q4. The major product of the reaction of 1-propene with HBr is

   • A) 1-Bromopropane
   • B) 2-Bromopropane
   • C) 1,2-Dibromopropane
   • D) Bromobenzene

   Answer: 2-Bromopropane

   Explanation: The reaction follows Markovnikov's rule, giving 2-bromopropane as the major product due to the more stable secondary carbocation.

5. Question 5

   Q5. Catalytic hydrogenation of alkenes results in

   • A) Alkanes
   • B) Alkynes
   • C) Alkenes
   • D) Alcohols

   Answer: Alkanes

   Explanation: Catalytic hydrogenation adds hydrogen to alkenes, forming alkanes. It's a reduction reaction.

6. Question 6

   Q6. Benzene is an example of

   • A) Aromatic hydrocarbon
   • B) Aliphatic hydrocarbon
   • C) Saturated hydrocarbon
   • D) Unsaturated aliphatic hydrocarbon

   Answer: Aromatic hydrocarbon

   Explanation: Benzene is aromatic due to its planar, ring-shaped molecule with delocalized electrons, following Hückel's rule.

7. Question 7

   Q7. The process of converting alkanes into alkyl halides by reaction with halogens in the presence of light is called

   • A) Halogenation
   • B) Hydrogenation
   • C) Dehydrogenation
   • D) Cracking

   Answer: Halogenation

   Explanation: Halogenation involves the substitution of hydrogen atoms in alkanes with halogen atoms in the presence of light.

8. Question 8

   Q8. The reaction of an alkene with cold, dilute KMnO4 results in the formation of

   • A) Diol
   • B) Alcohol
   • C) Aldehyde
   • D) Carboxylic acid

   Answer: Diol

   Explanation: Cold, dilute KMnO4 oxidizes alkenes to diols. It's a syn addition, resulting in a vicinal diol.

9. Question 9

   Q9. Which of the following alkanes has the highest boiling point?

   • A) Methane
   • B) Ethane
   • C) Propane
   • D) Butane

   Answer: Butane

   Explanation: Boiling points of alkanes increase with molecular weight due to increased London dispersion forces.

10. Question 10

    Q10. The hybridization of carbon atoms in alkynes is

    • A) sp
    • B) sp2
    • C) sp3
    • D) dsp2

    Answer: sp

    Explanation: Alkyne carbon atoms are sp hybridized, resulting in a linear geometry around the triple bond.

11. Question 11

    Q11. The reaction of 1-butyne with 2 moles of HCl gives

    • A) 1,1-Dichlorobutane
    • B) 2,2-Dichlorobutane
    • C) 1,2-Dichlorobutane
    • D) 2-Chlorobutane

    Answer: 2,2-Dichlorobutane

    Explanation: The addition follows Markovnikov's rule twice, resulting in 2,2-dichlorobutane.

12. Question 12

    Q12. Aromatic compounds are characterized by

    • A) Presence of a triple bond
    • B) Presence of a benzene ring
    • C) High reactivity
    • D) Saturated structure

    Answer: Presence of a benzene ring

    Explanation: Aromatic compounds are typically characterized by the presence of a benzene ring or similar structure with delocalized electrons.

13. Question 13

    Q13. The product of the reaction between benzene and nitric acid in the presence of sulfuric acid is

    • A) Nitrobenzene
    • B) Phenol
    • C) Benzaldehyde
    • D) Benzoic acid

    Answer: Nitrobenzene

    Explanation: Nitration of benzene gives nitrobenzene. The reaction is an electrophilic aromatic substitution.

14. Question 14

    Q14. Which of the following is a test for unsaturation?

    • A) Baeyer's test
    • B) Tollens' test
    • C) Fehling's test
    • D) Benedict's test

    Answer: Baeyer's test

    Explanation: Baeyer's test involves the reaction with cold, dilute KMnO4, decolorizing it if unsaturation is present.

15. Question 15

    Q15. The major product of the dehydrohalogenation of 2-bromobutane is

    • A) 1-Butene
    • B) 2-Butene
    • C) Isobutene
    • D) 1-Pentene

    Answer: 2-Butene

    Explanation: The reaction follows Saytzeff's rule, favoring the more substituted alkene, which is 2-butene.

16. Question 16

    Q16. The combustion of hydrocarbons produces

    • A) CO2 and H2O
    • B) CO and H2O
    • C) CO2 and H2
    • D) CO and H2

    Answer: CO2 and H2O

    Explanation: Complete combustion of hydrocarbons yields CO2 and H2O, releasing energy.

17. Question 17

    Q17. The reaction of ethyne with HgSO4/H2SO4 gives

    • A) Acetaldehyde
    • B) Ethanol
    • C) Acetone
    • D) Ethanoic acid

    Answer: Acetaldehyde

    Explanation: The reaction involves the hydration of ethyne to form acetaldehyde, catalyzed by HgSO4 in acidic medium.

18. Question 18

    Q18. The process of breaking large hydrocarbon molecules into smaller ones is called

    • A) Cracking
    • B) Reforming
    • C) Isomerization
    • D) Alkylation

    Answer: Cracking

    Explanation: Cracking involves breaking larger hydrocarbons into smaller, more useful hydrocarbons, often under thermal or catalytic conditions.

19. Question 19

    Q19. The addition of HBr to an unsymmetrical alkene in the presence of peroxide results in

    • A) Markovnikov product
    • B) Anti-Markovnikov product
    • C) Rearranged product
    • D) No reaction

    Answer: Anti-Markovnikov product

    Explanation: The presence of peroxide initiates a free-radical mechanism, resulting in the anti-Markovnikov addition of HBr.

20. Question 20

    Q20. Benzene reacts with chlorine in the presence of AlCl3 to give

    • A) Chlorobenzene
    • B) Dichlorobenzene
    • C) Hexachlorobenzene
    • D) Benzene hexachloride

    Answer: Chlorobenzene

    Explanation: The reaction is an electrophilic aromatic substitution, resulting in chlorobenzene. AlCl3 acts as a catalyst.