Bromine Test Identifies Unsaturation

Steps:

• Recall that unsaturated organic compounds contain double or triple bonds, reactive with halogens like bromine.
• Note the bromine test: aqueous bromine (orange-brown) adds across C=C bonds, forming colourless products.
• Evaluate choices: decolourisation specifically indicates addition reaction at unsaturated sites.
• Eliminate options lacking direct link to unsaturation, confirming A as the indicator.

Why A is correct:

• Unsaturated compounds undergo electrophilic addition with Br₂, decolourising the reddish-brown solution as colourless dibromide forms (e.g., C₂H₄ + Br₂ → C₂H₄Br₂).

Why the others are wrong:

• B: Sweet smell is common in many organics (e.g., alcohols, esters) but unrelated to saturation.
• C: Solvent properties depend on polarity, not saturation (e.g., both hexane and hexene dissolve organics).
• D: CO₂ production occurs in combustion of all carbon-containing compounds, saturated or not.

Final answer: A