Classifying CH4, C2H6, and C2H4 as hydrocarbons

Steps:

• Identify compounds: CH4 (methane, alkane), C2H6 (ethane, alkane), C2H4 (ethene, alkene).
• Note composition: All consist solely of carbon and hydrogen atoms.
• Apply definition: Hydrocarbons are organic compounds with only C and H.
• Test options: Only D fits all three universally.

Why D is correct:

• Hydrocarbons are defined as organic compounds containing only carbon and hydrogen, matching the formulas CH4, C2H6, and C2H4.

Why the others are wrong:

• A: CH4 and C2H6 (saturated) do not decolorize bromine water; only unsaturated C2H4 does.
• B: C2H4 is unsaturated due to its carbon-carbon double bond.
• C: CH4 and C2H6 are saturated alkanes with single bonds only.

Final answer: D