Identifying the structure of ethanoic anhydride

Steps:

• Recall that ethanoic anhydride is the dehydrated form of ethanoic acid, with formula (CH₃CO)₂O.
• Examine each option for the anhydride functional group: two acyl groups linked by an oxygen atom.
• Verify the carbon-oxygen-carbon linkage without hydroxyl groups typical of carboxylic acids.
• Confirm the molecular formula matches C₄H₆O₃ with correct bonding.

Why B is correct:

• Option B shows the exact structure CH₃C(O)OC(O)CH₃, matching the definition of an acid anhydride as RCO- O -COR'.

Why the others are wrong:

• A depicts an ester (CH₃COOCH₃), with single carbonyl and alkoxy group, not dual acyl linkage.
• C shows ethanoic acid (CH₃COOH), featuring a hydroxyl group instead of anhydride bridge.
• D represents a symmetric ether (CH₃OCH₃), lacking carbonyl groups entirely.

Final answer: B