Chapter Exam

Chapter-8 Aldehydes — Online MCQ Test

Q: What is the general structure of an aldehyde?

Answer: B. R-CHO — Aldehydes contain a carbonyl group (C=O) bonded to at least one hydrogen atom, represented as R-CHO where R is an alkyl or aryl group.

Q: Which compound is a ketone?

Answer: B. Propanone — Propanone (CH₃-CO-CH₃) is a ketone with the carbonyl group between two carbon atoms, whereas propanal is an aldehyde.

Q: Which carbonyl compound is most polar?

Answer: B. Formaldehyde — Formaldehyde (HCHO) is the smallest aldehyde with the highest electronegativity difference between C=O and the least steric hindrance, making it most polar.

Q: Scenario: A compound shows positive Tollens' test and positive iodoform test. What can be concluded?

Answer: B. It is acetaldehyde — Acetaldehyde (CH₃CHO) gives a positive Tollens' test (it's an aldehyde) and a positive iodoform test (has CH₃- group adjacent to carbonyl), making it the compound that satisfies both criteria.

CHEMISTRY · Grade 12 · CBSE(NCERT)

Practice Chapter-8 Aldehydes with a free chapter-wise online MCQ test for CBSE(NCERT) Grade 12 CHEMISTRY. This chapter covers: Ketones and Carboxylic Acids preparation - properties - acidity - basicity - reaction mechanisms. AI-generated questions from basic to board-exam level, with instant results and explanations.

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Chapter-8 Aldehydes — Important Questions & Answers (FAQ)

Frequently asked questions from CBSE(NCERT) Grade 12 CHEMISTRY — Chapter-8 Aldehydes, with answers and explanations. These are sample questions; the exam has its own separate question set.

What is the general structure of an aldehyde?

A. R-CO-R'
B. R-CHO ✓
C. R-COOH
D. R-OH

Answer: B. R-CHO
Aldehydes contain a carbonyl group (C=O) bonded to at least one hydrogen atom, represented as R-CHO where R is an alkyl or aryl group.

Which compound is a ketone?

A. Propanal
B. Propanone ✓
C. Propanoic acid
D. Propanol

Answer: B. Propanone
Propanone (CH₃-CO-CH₃) is a ketone with the carbonyl group between two carbon atoms, whereas propanal is an aldehyde.

Which carbonyl compound is most polar?

A. Benzaldehyde
B. Formaldehyde ✓
C. Acetone
D. Hexanal

Answer: B. Formaldehyde
Formaldehyde (HCHO) is the smallest aldehyde with the highest electronegativity difference between C=O and the least steric hindrance, making it most polar.

Scenario: A compound shows positive Tollens' test and positive iodoform test. What can be concluded?

A. It is a methyl ketone
B. It is acetaldehyde ✓
C. It contains both aldehyde and methyl ketone groups
D. It is formaldehyde

Answer: B. It is acetaldehyde
Acetaldehyde (CH₃CHO) gives a positive Tollens' test (it's an aldehyde) and a positive iodoform test (has CH₃- group adjacent to carbonyl), making it the compound that satisfies both criteria.

What happens when a mixture of acetaldehyde and formaldehyde is treated with dilute NaOH?

A. Only formaldehyde undergoes Cannizzaro reaction
B. Both undergo aldol condensation
C. Only acetaldehyde undergoes aldol condensation
D. Formaldehyde undergoes Cannizzaro reaction while acetaldehyde undergoes aldol condensation ✓

Answer: D. Formaldehyde undergoes Cannizzaro reaction while acetaldehyde undergoes aldol condensation
Formaldehyde (having no α-hydrogen) undergoes the Cannizzaro reaction producing methanol and formic acid, while acetaldehyde (with α-hydrogen) undergoes aldol condensation with itself or formaldehyde.