Match List-I with List-II.
| List-I (Reaction) | List-II (Reagent and conditions) |
|---|---|
| (A) Aldol reaction of ethanal | (I) Freshly prepared ammoniacal silver nitrate, warming |
| (B) Cannizzaro reaction of benzaldehyde | (II) Dilute NaOH |
| (C) Conversion of benzaldehyde into m-nitrobenzaldehyde | (III) \( \ce{HNO3}/\ce{H2SO4} \), 273–283 K |
| (D) Tollens’ test of an aldehyde | (IV) Concentrated NaOH, heating |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A-II, B-IV, C-III, D-I
The same base can start different reactions: its concentration and whether the aldehyde has an α-hydrogen decide whether an aldol or a Cannizzaro reaction takes place.
(A) Aldol reaction of ethanal — This matches (II) Dilute NaOH. Ethanal has α-hydrogens, and dilute alkali acts as the catalyst:
\( \displaystyle \ce{2CH3CHO <=>[\text{dil. NaOH}] CH3CH(OH)CH2CHO} \)
(B) Cannizzaro reaction of benzaldehyde — This matches (IV) Concentrated NaOH, heating. Benzaldehyde has no α-hydrogen, so on heating with concentrated alkali one molecule is reduced and another oxidised:
\( \displaystyle \ce{2C6H5CHO + NaOH} \xrightarrow{\Delta} \ce{C6H5CH2OH + C6H5COONa} \)
(C) Benzaldehyde into m-nitrobenzaldehyde — This matches (III) HNO3/H2SO4, 273–283 K. This is electrophilic substitution (nitration) at the ring, and the carbonyl group directs the nitro group to the meta position.
(D) Tollens’ test of an aldehyde — This matches (I) Freshly prepared ammoniacal silver nitrate, warming. Tollens’ reagent is ammoniacal silver nitrate; on warming, the aldehyde is oxidised and silver metal is deposited as a bright silver mirror.
NCERT (2026-27 edition):
8.4 Chemical Reactions – “(i) Aldol condensation: Aldehydes and ketones having at least one α-hydrogen undergo a reaction in the presence of dilute alkali as catalyst to form β-hydroxy aldehydes (aldol) or β-hydroxy ketones (ketol), respectively.”
“(i) Cannizzaro reaction: Aldehydes which do not have an α-hydrogen atom, undergo self oxidation and reduction (disproportionation) reaction on heating with concentrated alkali.”
“(ii) Electrophilic substitution reaction: Aromatic aldehydes and ketones undergo electrophilic substitution at the ring in which the carbonyl group acts as a deactivating and meta-directing group.”
“(i) Tollens’ test: On warming an aldehyde with freshly prepared ammoniacal silver nitrate solution (Tollens’ reagent), a bright silver mirror is produced due to the formation of silver metal.”
