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Organic Chemistry — Some Basic Principles and Techniques — NEET & JEE MCQs with answers
Unit 8 introduces the structural framework of organic chemistry: the tetravalence of carbon and hybridisation ($sp^3$, $sp^2$, $sp$), structural representation of organic molecules, classification by functional group and homologous series, IUPAC nomenclature, isomerism (structural and stereo), basics of reaction mechanisms (bond fission, reactive intermediates, electronic effects), and purification and analysis techniques (chromatography, qualitative and quantitative element analysis).
Topics in this chapter
- 8.1 General Introduction
- 8.2 Tetravalence of Carbon: Shapes of Organic Compounds and Nomenclature of Alkyl Groups
- 8.3 Structural Representation of Organic Compounds
- 8.4 Classification of Organic Compounds
- 8.5 Nomenclature of Organic Compounds
- 8.6 Isomerism
- 8.7 Fundamental Concepts in Organic Reaction Mechanism
- 8.8 Methods of Purification of Organic Compounds
- 8.9 Qualitative Analysis of Organic Compounds
- 8.10 Quantitative Analysis
Free practice questions
The unique property of carbon by which it forms covalent bonds with other carbon atoms is called:
- A. Hybridisation
- B. Tetravalency
- C. Catenation
- D. Resonance
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Answer: C — As stated in the NCERT introduction to Unit 8, carbon has the unique property called catenation due to which it forms covalent bonds with other carbon atoms.
NCERT Class 11 Chemistry · Ch 8 · 8.1 General Introduction
The two broad structural classes into which organic compounds are first divided are:
- A. Polar and non-polar compounds
- B. Acyclic (open chain) and cyclic (closed chain) compounds
- C. Benzenoid and non-benzenoid compounds
- D. Saturated and unsaturated compounds
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Answer: B — Organic compounds are broadly classified into (i) acyclic or open chain compounds and (ii) cyclic or closed chain (ring) compounds.
NCERT Class 11 Chemistry · Ch 8 · 8.4 Classification of Organic Compounds
In metamerism, the compounds involved have the same:
- A. molecular formula but different functional groups
- B. molecular formula and the same functional group, but different alkyl chains around it
- C. functional group at different positions on the same chain
- D. spatial arrangement but different connectivity
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Answer: B — Metamers have the same molecular formula and the same functional group, but differ in the alkyl chains attached on either side of that functional group.
NCERT Class 11 Chemistry · Ch 8 · 8.6.1 Metamerism
In a conjugated system such as 1,3-butadiene or nitrobenzene, the pi-electrons are:
- A. removed from the molecule
- B. fully localised on individual double bonds
- C. converted into sigma electrons
- D. delocalised, and the system develops polarity
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Answer: D — In conjugated systems (alternate single and double bonds), the pi-electrons are delocalised and the system develops polarity; examples are 1,3-butadiene, aniline and nitrobenzene.
NCERT Class 11 Chemistry · Ch 8 · 8.7 Fundamental Concepts in Organic Reaction Mechanism
While detecting hydrogen, the water formed turns anhydrous copper sulphate blue. The blue substance formed is:
- A. Hydrated copper sulphate, CuSO4·5H2O
- B. Copper hydroxide, Cu(OH)2
- C. Copper carbonate, CuCO3
- D. Copper(I) oxide, Cu2O
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Answer: A — Water combines with anhydrous (white) copper sulphate to form hydrated copper sulphate, CuSO4·5H2O, which is blue: 5H2O + CuSO4 → CuSO4·5H2O.
NCERT Class 11 Chemistry · Ch 8 · 8.9 Qualitative Analysis of Organic Compounds
Unsaturated hydrocarbons are those which contain at least one:
- A. ionic bond
- B. carbon-carbon double or triple bond
- C. carbon-hydrogen single bond
- D. carbon-carbon single bond only
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Answer: B — NCERT states unsaturated hydrocarbons are those which contain at least one carbon-carbon double or triple bond.
NCERT Class 11 Chemistry · Ch 8 · 8.5 Nomenclature - Alkanes and Alkyl Groups
For differential extraction to work, the organic solvent and the aqueous solution must be:
- A. Of equal boiling points
- B. Both volatile and steam volatile
- C. Completely miscible with each other
- D. Immiscible with each other
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Answer: D — In differential extraction, the organic solvent and the aqueous solution should be immiscible with each other so that they form two distinct layers, which can be separated by a separatory funnel.
NCERT Class 11 Chemistry · Ch 8 · 8.8 Methods of Purification of Organic Compounds
A hydrocarbon that contains at least one carbon–carbon double or triple bond is called:
- A. An unsaturated hydrocarbon
- B. An alkane
- C. A paraffin
- D. A saturated hydrocarbon
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Answer: A — Unsaturated hydrocarbons are those which contain at least one carbon-carbon double or triple bond, in contrast to saturated hydrocarbons (only single bonds).
NCERT Class 11 Chemistry · Ch 8 · 8.5 Nomenclature of Organic Compounds
0.25 g of an organic compound on combustion gave 0.225 g of water. The percentage of hydrogen in the compound is:
- A. 5.0%
- B. 90.0%
- C. 9.0%
- D. 10.0%
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Answer: D — %H = (2/18) x (mass H2O / mass compound) x 100 = (2/18) x (0.225/0.25) x 100 = 0.1111 x 0.9 x 100 = 10.0%.
NCERT Class 11 Chemistry · Ch 8 · 8.10 Quantitative Analysis
In a bond-line formula, a line junction at which three carbon-carbon lines meet (a branch point) represents a carbon bonded to how many hydrogen atoms?
- A. 1
- B. 2
- C. 3
- D. 0
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Answer: A — NCERT 8.3.1: each junction carbon carries enough hydrogens to complete its valency of four. A junction where three C–C bonds meet already has three bonds to carbon, so it needs only 1 hydrogen (a –CH< group).
NCERT Class 11 Chemistry · Ch 8 · 8.3 Structural Representation of Organic Compounds
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