Read the passage given and answer the question.
Phenol and alcohol have the same functional group (-OH) but phenols are stronger acids than alcohols due to the resonance stabilization of phenoxide ion than alkoxide ion \((-RO^-)\). Electron withdrawing groups tend to increase the acidic strength while electron releasing groups tend to decrease it.
What happens when ethylene glycol reacts with periodic acid?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Formaldehyde is produced
Periodic acid (HIO4) cleaves the C–C bond of a 1,2-diol (two –OH groups on neighbouring carbons). Each carbon that carried an –OH group ends up as a carbonyl group. In ethylene glycol (ethane-1,2-diol) both carbons are \( \ce{CH2OH} \), so each becomes a molecule of methanal (formaldehyde):
\( \ce{HOCH2-CH2OH + HIO4 -> 2HCHO + HIO3 + H2O} \)
Why the other options are incorrect
Option (2) Acetaldehyde is produced — Incorrect. Acetaldehyde (\( \ce{CH3CHO} \)) has two carbons in one molecule; the cleavage breaks the only C–C bond of the glycol, so a two-carbon product cannot form.
Option (3) Formic acid is produced — Incorrect. \( \ce{HIO4} \) stops at the carbonyl stage for a \( \ce{CH2OH} \) end; formic acid forms only from a CHOH carbon bonded to two other –OH-bearing carbons, as the middle carbon of glycerol.
Option (4) Acetic acid is produced — Incorrect. \( \ce{HIO4} \) breaks the only C–C bond, so no two-carbon product such as \( \ce{CH3COOH} \) can form; each \( \ce{CH2OH} \) end gives HCHO.
Note: The question is from beyond the NCERT textbook.