Read the Passage carefully and answer the Questions.
Carbonyl compounds such as aldehydes, ketones, and carboxylic acids play an important role in the biochemical process of plants and animal kingdom. Many aldehydes and ketones find applications in dye, perfumery and other industries. The carbonyl carbon atom is \( sp^2 \)-hybridized forming three sigma and one pi-bond with oxygen. C-O bonds are polar bond due to high electronegativity of oxygen than carbon. Hence the carbonyl carbon behaves as an electrophilic center and oxygen as a nucleophilic centre. Primary and secondary alcohols yield aldehydes and ketones respectively upon oxidation with variety of oxidizing agents. The boiling points of aldehydes and ketones differ from hydrocarbons and ethers. Aldehydes and ketones undergo nucleophilic addition reaction due to presence of electrophilic carbonyl carbon. Nucleophile and a proton add across the carbon oxygen double bond.
In polar C-O bond in carbonyl compounds, the nature of carbon and oxygen atom is
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → The carbon atom acts as a Lewis acid and the oxygen atom acts as Lewis base.
A Lewis acid is an electron-pair acceptor and a Lewis base is an electron-pair donor. In the carbonyl group, oxygen is more electronegative than carbon, so the C=O bond is polarised:
\( \displaystyle \ce{>C^{\delta+}=O^{\delta-}} \)
The carbon atom carries a partial positive charge and is attacked by nucleophiles, so it is an electrophilic centre and behaves as a Lewis acid. The oxygen atom carries a partial negative charge and two lone pairs, so it is a nucleophilic centre and behaves as a Lewis base; for example, it accepts a proton from an acid.
Why the other options are incorrect
Option (2) Both carbon and oxygen atoms act as Lewis acid — Incorrect. The oxygen atom is electron-rich and has lone pairs; it donates, not accepts, an electron pair.
Option (3) Both carbon and oxygen atoms act as Lewis base — Incorrect. The carbon atom is electron-deficient; it accepts the electron pair of a nucleophile.
Option (4) The carbon atom acts as an Lewis base and the oxygen atom acts as a Lewis acid. — Incorrect. This reverses the roles; the polarity of the bond puts the positive end on carbon and the negative end on oxygen.
NCERT (2026-27 edition):
Structure of the Carbonyl Group – …
