Carboxylic Acid Functional Group in Fatty Acid Salts

Steps:

• Carboxylic acids contain the -COOH functional group, where carbon is double-bonded to oxygen and single-bonded to OH.
• Review options to match the standard carboxyl group formula: -COOH.
• Magnesium, a +2 ion, forms salts like (RCOO)₂Mg by replacing two H⁺ from two RCOOH molecules.
• Thus, 2 moles of fatty acid react with 1 mole of magnesium to neutralize and form the salt.

Why B is correct:

• -COOH is the defined functional group for carboxylic acids (general formula R-COOH); however, the stoichiometry is 2:1, not 1:1 as listed—likely a question ambiguity, making B the best match for the group.

Why the others are wrong:

• A: -COH is not a recognized functional group; incorrect formula.
• C: -CHOH represents an alcohol (-OH on carbon), not carboxylic acid.
• D: -CHOH is alcohol functional group; wrong despite correct 2:1 ratio.

Final answer: B