Organic chemistry is the branch of chemistry that deals with the study of carbon-containing compounds and their properties, structures, reactions, and uses. This chapter explains the unique bonding properties of carbon, classification of organic compounds, functional groups, homologous series, and the basics of IUPAC nomenclature. It also covers important classes of hydrocarbons such as alkanes, alkenes, and alkynes, their sources, properties, and reactions including combustion, substitution, and addition. Additionally, it introduces isomerism, polymers, and the role of organic compounds in daily life and industry.
1. Which element is the basis of organic chemistry?
- A. Hydrogen
- B. Oxygen
- C. Carbon ✅
- D. Nitrogen
Explanation: Organic chemistry is primarily concerned with carbon and its compounds.
2. Why can carbon form such a large number of compounds?
- A. It is the most reactive element
- B. It can form four covalent bonds and catenate ✅
- C. It has high metallic character
- D. It is always ionic
Explanation: Carbon’s tetravalency and ability to form chains (catenation) allow it to create a vast variety of compounds.
3. Which of the following is an example of a saturated hydrocarbon?
- A. Ethene
- B. Propane ✅
- C. Ethyne
- D. Benzene
Explanation: Propane is an alkane, containing only single bonds between carbon atoms.
4. The general formula for alkanes is:
- A. CnH2n
- B. CnH2n-2
- C. CnH2n+2 ✅
- D. CnHn+2
Explanation: Alkanes are saturated hydrocarbons with the general formula CnH2n+2.
5. Which type of bond is present in alkenes?
- A. Only single bonds
- B. At least one double bond ✅
- C. At least one triple bond
- D. Aromatic ring
Explanation: Alkenes are unsaturated hydrocarbons with one or more C=C double bonds.
6. Which of the following is an alkyne?
- A. Butane
- B. Butene
- C. Butyne ✅
- D. Benzene
Explanation: Alkynes are hydrocarbons with at least one triple bond between carbon atoms; butyne is an example.
7. What is the functional group in alcohols?
- A. –CHO
- B. –COOH
- C. –OH ✅
- D. –NH2
Explanation: Alcohols contain the hydroxyl (–OH) functional group.
8. Which functional group is present in carboxylic acids?
- A. –OH
- B. –COO–
- C. –COOH ✅
- D. –C=O
Explanation: Carboxylic acids contain the carboxyl group (–COOH).
9. The compounds having the same molecular formula but different structures are called:
- A. Polymers
- B. Isotopes
- C. Isomers ✅
- D. Allotropes
Explanation: Isomers differ in structural arrangement of atoms while having the same molecular formula.
10. Which is the correct IUPAC name for CH3–CH2–CH3?
- A. Ethane
- B. Propane ✅
- C. Butane
- D. Methane
Explanation: Three carbon atoms with single bonds correspond to propane in IUPAC nomenclature.
11. Which process converts ethene to ethane?
- A. Dehydration
- B. Hydrogenation ✅
- C. Polymerization
- D. Substitution
Explanation: Hydrogenation adds hydrogen to double bonds, converting alkenes to alkanes.
12. What is produced when alkanes undergo complete combustion?
- A. CO only
- B. CO2 and H2
- C. CO2 and H2O ✅
- D. CO and H2O
Explanation: Complete combustion of hydrocarbons produces carbon dioxide and water.
13. Which polymer is formed from ethene?
- A. Polyvinyl chloride
- B. Polyethylene ✅
- C. Polystyrene
- D. Teflon
Explanation: Polymerization of ethene yields polyethylene, a common plastic.
14. What is the main source of hydrocarbons?
- A. Coal only
- B. Natural gas only
- C. Petroleum and natural gas ✅
- D. Plants only
Explanation: Petroleum and natural gas are the main sources of hydrocarbons used in fuels and chemicals.
15. Which reaction type occurs when chlorine replaces hydrogen in methane?
- A. Addition
- B. Substitution ✅
- C. Elimination
- D. Polymerization
Explanation: Halogen substitution replaces hydrogen atoms with halogen atoms in alkanes.
16. Benzene belongs to which class of hydrocarbons?
- A. Alkane
- B. Alkyne
- C. Aromatic ✅
- D. Alkene
Explanation: Benzene is an aromatic hydrocarbon with a cyclic structure and delocalized π electrons.
17. Which of the following is NOT a property of alkanes?
- A. Non-polar
- B. Saturated
- C. Highly reactive with acids at room temperature ✅
- D. Combustible
Explanation: Alkanes are relatively unreactive toward acids and bases at room temperature.
18. Which gas is formed during incomplete combustion of hydrocarbons?
- A. CO2
- B. CO ✅
- C. CH4
- D. H2
Explanation: Incomplete combustion forms carbon monoxide, a poisonous gas.
19. The simplest alkyne is:
- A. Ethane
- B. Ethyne ✅
- C. Propyne
- D. Methyne
Explanation: Ethyne (acetylene) has the formula C2H2 and one triple bond.
20. Which property is common to all hydrocarbons?
- A. They are soluble in water
- B. They are combustible ✅
- C. They are ionic
- D. They are always solid
Explanation: Hydrocarbons burn to produce heat energy, making them useful fuels.