NCERT Class 10 Science — Chapter 4: Carbon and its Compounds

The correct option is C2H2.

Explanation

Hydrocarbons are organic compounds consisting entirely of hydrogen and carbon. They are classified based on the type of bonding between carbon atoms:

• Saturated Hydrocarbons (Alkanes): Contain only single bonds between carbon atoms. They follow the general formula C_nH_2n+2.
• Unsaturated Hydrocarbons (Alkenes and Alkynes): Contain at least one double or triple bond between carbon atoms. Alkenes follow C_nH_2n, and Alkynes follow C_nH_2n-2.

Analysis of Options:

• C2H2 C₂H₂ (Ethyne): This fits the general formula for alkynes (C_nH_2n-2 where n=2). It contains a carbon-carbon triple bond (H-C≡C-H), making it unsaturated.
• C2H6 C₂H₆ (Ethane): This fits the general formula for alkanes (C_nH_2n+2 where n=2). It contains only single bonds, making it saturated.
• CH4 CH₄ (Methane): This fits the general formula for alkanes (where n=1). It contains only single bonds, making it saturated.
• C3H8 C₃H₈ (Propane): This fits the general formula for alkanes (where n=3). It contains only single bonds, making it saturated.

Key Takeaway:

Unsaturated hydrocarbons are identified by the presence of multiple bonds (double or triple) between carbon atoms, which results in fewer hydrogen atoms compared to a saturated hydrocarbon with the same number of carbon atoms.