Citric acid's molecular formula from structure

Steps:

• Identify citric acid as 2-hydroxypropane-1,2,3-tricarboxylic acid, a Krebs cycle intermediate.
• Examine its structure: a propane chain with three -COOH groups and one -OH on the central carbon.
• Count carbons: 6 from the chain and carboxyls.
• Tally atoms: 6 C, 8 H (from chain, -OH, and acids), 7 O (from three -COOH and one -OH).

Why A is correct:

• C₆H₈O₇ exactly matches the atom count in citric acid's established structure per IUPAC nomenclature.

Why the others are wrong:

• B: C₆H₅O₇ undercounts hydrogens by 3, ignoring those in the hydroxyl and acid groups.
• C: C₆H₈O₆ lacks one oxygen required for the third carboxyl group.
• D: C₆H₈O₈ adds an extra oxygen absent from the actual molecule.

Final answer: A