37 past paper MCQs on Reactions of Aldehydes and Ketones, from the Aldehydes and Ketones unit of MDCAT Chemistry. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.
1.Which of the following is also called the silver mirror test? (MDCAT 2022)
Correct answer: (d) Tollen's reagent test
The aldehyde reduces the silver ion of Tollen's reagent to metallic silver, which plates the tube.
2.The blue colour of Fehling's solution is changed to red when warmed with an aldehyde due to the formation of: (MDCAT 2024)
Correct answer: (b) $\mathrm{Cu_2O}$
The aldehyde reduces copper(II) to a red precipitate of copper(I) oxide.
3.The reaction of HCN with formaldehyde is a: (MDCAT 2024)
Correct answer: (a) nucleophilic addition reaction
The cyanide ion adds to the carbon of the polar carbonyl group, giving a cyanohydrin.
4.Acetaldehyde undergoes oxidation to produce acetic acid, In this reaction oxidizing agent used is: (UHS MDCAT 2025)
Correct answer: (c) K2Cr2O7
Acidified potassium dichromate oxidizes the aldehyde to the acid; the hydrides are reducing agents.
5.Methanol is produced by reduction of (UHS MDCAT 2025)
Correct answer: (a) Formaldehyde
Reducing the simplest aldehyde, formaldehyde, gives the simplest alcohol, methanol.
6.Polymerization of HCHO and CH3CHO occurs in the presence of: (NUMS MDCAT 2025)
Correct answer: (a) Conc. H2SO4
Concentrated sulphuric acid polymerizes formaldehyde and acetaldehyde to trioxane and paraldehyde.
7.During Clemmenson reduction of aldehyde and ketone, carbonyl group into alkane group is carried out with: (SIBA MDCAT 2025)
Correct answer: (c) Zn/Hg conc.HCl
Clemmensen reduction uses zinc amalgam with concentrated hydrochloric acid to take the carbonyl down to a methylene group.
8.The blue color of Fehling solution is changed to red when warmed with an aldehyde due to formation of which of the following? (UHS MDCAT 2024)
Correct answer: (b) Cu2O
The aldehyde reduces the copper(II) of Fehling’s solution to a red precipitate of copper(I) oxide.
9.Reaction of HCN with formaldehyde is a: (UHS MDCAT 2024)
Correct answer: (a) Nucleophilic addition reaction
The cyanide ion attacks the electron poor carbonyl carbon, so the step is nucleophilic addition.
10.Compound A + I2 + Na2CO3 → Compound B + RCOONa + NaI + H2O. Identify compound B: (NUMS MDCAT 2024)
Correct answer: (a) Acetone
A methyl ketone gives iodoform with iodine and alkali, and the ketone here is acetone.
11.When Phenol reacts with formaldehyde, which of the following product is produced? (UHS MDCAT 2023)
Correct answer: (a) Adduct
The ring attacks the carbonyl carbon and an addition product, the adduct, is formed first.
12.Which of the following is also called silver mirror test? (UHS MDCAT 2023)
Correct answer: (d) Tollen's reagent test
Tollens’ reagent leaves a mirror of silver on the wall of the tube.
13.Catalytic reduction of Aldehyde & Ketone forms: (SZABMU MDCAT 2023)
Correct answer: (a) Alcohol
Hydrogen over a metal catalyst takes the carbonyl group down to an alcohol.
14.When Aldehyde reacts with 50% NaOH, this reaction is called as: (SZABMU MDCAT 2023)
Correct answer: (d) Cannizarros’s reaction
An aldehyde with no alpha hydrogen disproportionates in strong alkali, which is the Cannizzaro reaction.
15.The appearance of a silver mirror in Toliens test indicates the presence of which of the following? (UHS MDCAT 2023)
Correct answer: (b) An aldehyde
Only an aldehyde reduces Tollens’ reagent and leaves the silver mirror.
16.AcetaIs are: (PMC MDCAT 2022)
Correct answer: (a) Diethers
An acetal has two alkoxy groups on the same carbon, so it is a diether.
17.When two moles of acetone are treated with a base, the product is? (PMC MDCAT 2022)
Correct answer: (b) 4-hydroxy-4 methyl-2-pentanone
Base catalysed aldol condensation of two acetone molecules gives diacetone alcohol.
18.Formaldehyde reacts with which one of the following to give primary alcohols (PMC MDCAT 2022)
Correct answer: (c) Grignard's reagant
A Grignard reagent adds to formaldehyde and the product hydrolyses to a primary alcohol.
19.Aldol products upon heating undergoes: (PMC MDCAT 2022)
Correct answer: (b) Dehydration
The aldol loses water on heating and leaves an unsaturated carbonyl compound.
20.lodoform test is used to check the presence of: (PMC MDCAT 2022)
Correct answer: (b) Carbonyl compounds
The iodoform test picks out a methyl ketone or an alcohol that oxidizes to one.
21.The carbanion attacks the molecule of another carbonyl compound to form: (PMC MDCAT 2022)
Correct answer: (b) aldol
The carbanion adds to the carbonyl carbon of another molecule and the product is an aldol.
22.Fehling’s solution is: (PMC MDCAT 2022)
Correct answer: (c) Alkaline cupric tartarate complex ion
Fehling’s solution is copper(II) held in alkaline solution by tartrate.
23.The identification test for Ketone is: (NUMS MDCAT 2022)
Correct answer: (c) Sodium Nitro Prusside Test
Sodium nitroprusside gives a red colour with a ketone but not with an aldehyde.
24.Which of the following compounds give a positive silver mirror test? (PMC Practice 2021)
Correct answer: (d) All of these options are correct
All three are aldehydes, and every aldehyde reduces Tollens’ reagent.
25.Which of the following reagent is used to separate and purify carbonyl and non carbonyl compounds? (PMC MDCAT 2020)
Correct answer: (c) NaHSO3
Sodium bisulphite gives a crystalline addition product with aldehydes and methyl ketones, which is then hydrolysed back.
26.Identification tests for functional groups of organic compounds are associated with specific observations. Tollen’s reagent is an ammoniacal silver nitrate solution, which is used for the identification of a functional group X with an observation O. Identify X and O. (UHS MDCAT 2019)
Correct answer: (a) X = Aldehyde O = Silver mirror
Only an aldehyde reduces Tollens’ reagent, leaving a mirror of silver.
27.Ketones can be made by oxidation of: (UHS MDCAT 2019)
Correct answer: (c) Secondary Alcohols
A secondary alcohol has one hydrogen on the carbinol carbon, so oxidation stops at the ketone.
28.Which type of reaction takes place when a carbonyl compound is treated with a mixture of NaCN and an acid? (UHS MDCAT 2019)
Correct answer: (c) Nucleophilic addition reaction
The cyanide ion attacks the electron poor carbonyl carbon, so the step is nucleophilic addition.
29.Which of the following will give a positive test with Tollen’s reagent? (UHS MDCAT 2019)
Correct answer: (c) Aldehydes
Only an aldehyde reduces Tollens’ reagent.
30.Which of the following compounds will give a secondary alcohol after reaction with NaBH4? (UHS MDCAT 2019)
Correct answer: (a) CH3COCH3
Sodium borohydride reduces a ketone to a secondary alcohol.
31.Which one of the following reagents is used to distinguish between aldehydes and ketones? (UHS MDCAT 2018)
Correct answer: (b) Tollen’s Reagent
Tollens’ reagent leaves a silver mirror with an aldehyde and nothing with a ketone.
32.Which compound will be produced by the oxidation of ethanal by acidified K2Cr2O7 ? (UHS MDCAT 2018)
Correct answer: (c) Ethanoic acid
Acidified dichromate oxidizes the aldehyde on to the acid.
33.Which mechanism of reactions is shown by carbonyl compounds? (UHS MDCAT 2018)
Correct answer: (d) Nucleophilic addition
The carbonyl carbon is electron poor, so a nucleophile adds to it.
34.To distinguish aldehyde from ketone which solution is used: (UHS MDCAT 2017)
Correct answer: (b) Fehling’s solution
Fehling’s solution gives a red precipitate with an aldehyde and nothing with a ketone.
35.Which reagent is responsible for the conversion of ketone to secondary alcohol: (UHS MDCAT 2017)
Correct answer: (b) NaBH4
Sodium borohydride reduces a ketone to a secondary alcohol.
36.Both aldehyde and ketones give _____: (UHS MDCAT 2017)
Correct answer: (b) 2,4-DNPH test
2,4-dinitrophenylhydrazine gives an orange precipitate with any carbonyl compound.
37.Which one of the following is an appropriate indication of positive iodoform test? (UHS MDCAT 2016)
Correct answer: (d) Yellow crystal
Iodoform comes down as yellow crystals with the smell of antiseptic.