The Hydrocarbons chapter in Punjab Board Class 10 Chemistry focuses on compounds made entirely of carbon and hydrogen, their types, properties, sources, and uses. It explains the classification of hydrocarbons into alkanes, alkenes, and alkynes, along with their general formulas, structures, and important reactions. The chapter also covers concepts such as isomerism, sources of hydrocarbons like petroleum and natural gas, fractional distillation, and the significance of hydrocarbons in daily life and industry.
1. Which elements are present in hydrocarbons?
- A. Carbon, hydrogen, and oxygen
- B. Carbon and hydrogen only ✅
- C. Carbon, hydrogen, and nitrogen
- D. Carbon and oxygen only
Explanation: Hydrocarbons are organic compounds containing only carbon and hydrogen atoms.
2. Which type of hydrocarbon contains only single covalent bonds?
- A. Alkenes
- B. Alkynes
- C. Alkanes ✅
- D. Aromatics
Explanation: Alkanes are saturated hydrocarbons containing only single covalent bonds between carbon atoms.
3. What is the general formula of alkanes?
- A. CnH2n
- B. CnH2n−2
- C. CnH2n+2 ✅
- D. CnHn
Explanation: The general formula of alkanes is CnH2n+2 for straight-chain hydrocarbons.
4. Which hydrocarbon series is known as olefins?
- A. Alkenes ✅
- B. Alkynes
- C. Aromatics
- D. Cycloalkanes
Explanation: Alkenes are unsaturated hydrocarbons with at least one double bond, historically called olefins.
5. What is the general formula for alkenes?
- A. CnH2n+2
- B. CnH2n ✅
- C. CnH2n−2
- D. CnHn
Explanation: Alkenes follow the formula CnH2n for straight-chain compounds.
6. Which hydrocarbon series is known as acetylenes?
- A. Alkenes
- B. Alkynes ✅
- C. Aromatics
- D. Cycloalkanes
Explanation: Alkynes are unsaturated hydrocarbons with at least one triple bond, historically called acetylenes.
7. Which reaction converts ethene to ethane?
- A. Substitution
- B. Hydrogenation ✅
- C. Combustion
- D. Polymerization
Explanation: Hydrogenation adds hydrogen to an alkene, converting it into an alkane.
8. Which reaction produces polymers from hydrocarbons?
- A. Hydrogenation
- B. Cracking
- C. Polymerization ✅
- D. Isomerization
Explanation: Polymerization links monomer units to form large molecules called polymers.
9. What is isomerism in hydrocarbons?
- A. Same formula, same structure
- B. Same molecular formula but different structural arrangement ✅
- C. Different formulas and structures
- D. Different formulas, same properties
Explanation: Isomers have the same molecular formula but differ in the arrangement of atoms.
10. Which fraction from petroleum contains the smallest hydrocarbons?
- A. Kerosene
- B. Petroleum gas ✅
- C. Diesel
- D. Fuel oil
Explanation: Petroleum gas contains the lightest hydrocarbons and is used as a fuel.
11. Which process breaks large hydrocarbon molecules into smaller ones?
- A. Polymerization
- B. Cracking ✅
- C. Hydrogenation
- D. Distillation
Explanation: Cracking decomposes heavy hydrocarbons into lighter, more useful products.
12. Which hydrocarbon is the main component of natural gas?
- A. Ethane
- B. Methane ✅
- C. Propane
- D. Butane
Explanation: Methane (CH4) is the major component of natural gas.
13. What is the product of complete combustion of hydrocarbons?
- A. Carbon dioxide and water ✅
- B. Carbon monoxide and water
- C. Carbon and water
- D. Carbon dioxide only
Explanation: Complete combustion produces CO2 and H2O with release of energy.
14. Which environmental problem is caused by incomplete combustion of hydrocarbons?
- A. Ozone layer depletion
- B. Carbon monoxide poisoning ✅
- C. Acid rain
- D. Global cooling
Explanation: Incomplete combustion forms CO, a toxic gas that binds with hemoglobin.
15. Which polymer is produced from ethene?
- A. PVC
- B. Polyethylene ✅
- C. Polystyrene
- D. Bakelite
Explanation: Polyethylene is formed by polymerizing ethene molecules.