AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
(C) Ethene (C₂H₄)
Ethene is an unsaturated hydrocarbon with a C=C double bond; it decolourises bromine water and undergoes hydrogenation with H₂ in the presence of a nickel catalyst.
(Note: Option (D) listed as C₂H₂/ethyne also fits, but among the named options, Ethene is the standard answer.)
The question tests knowledge of addition reactions. Only unsaturated hydrocarbons (alkenes/alkynes) decolourise bromine water (by adding Br₂ across the double/triple bond) and undergo hydrogenation. Methane, ethane, and propane are saturated; they do neither. The question's option list names "Ethene" as (C), making it the correct choice. Ethyne (C₂H₂) also qualifies chemically, but it is not among the named options (A–D) as stated in the question stem—the option (D) in the stem is "Propane."