Relevant Titles
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CBSE Class 11 MCQs — Reactions of Alkenes and Alkynes (NCERT Practice)
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Class 11 Chemistry Quiz: Addition, Elimination & Oxidation of Alkenes/Alkynes
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CBSE Test — Alkenes & Alkynes: Markovnikov, Anti-Markovnikov & Stereochemistry MCQs
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Reactions of Alkenes and Alkynes — CBSE Class 11 Online Practice Questions
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NCERT-Based Alkenes and Alkynes MCQs for CBSE Class 11 Board Prep
Introduction
Prepare confidently for CBSE Class 11 Chemistry with this focused NCERT-aligned test on Reactions of Alkenes and Alkynes, taken from Chapter 13: Hydrocarbons (Part C: Organic Chemistry). This practice set targets the reaction types and mechanisms that matter most for board exams: electrophilic and radical additions, hydroboration–oxidation, oxymercuration–demercuration, hydrogenation (including Lindlar and dissolving-metal reduction), halogenation, ozonolysis, and mechanisms that lead to carbocation rearrangements. Each multiple-choice question is crafted to reinforce conceptual understanding — regiochemistry (Markovnikov vs anti-Markovnikov), stereochemistry (syn vs anti addition), and the outcomes of different reagents and catalysts. Chemical formulas and reaction notations (e.g., H₂, Br₂, CO₂) are formatted for clarity. Use this 30-minute timed practice to identify weak spots, get instant feedback, and review concise explanations that map directly to NCERT learning objectives. Ideal for revision before tests or as a quick daily practice, this quiz helps you convert conceptual knowledge into reliable exam performance.
Sample MCQs (with Answers & Explanations)
Q1. Addition of HBr to propene (CH₃CH=CH₂) under normal ionic conditions gives:
A) 1-bromopropane (anti-Markovnikov)
B) 2-bromopropane (Markovnikov)
C) Propane only
D) No reaction
Answer: B) 2-bromopropane
Explanation: Ionic hydrohalogenation follows Markovnikov’s rule: H adds to the less substituted carbon, forming a more stable carbocation intermediate; Br attaches to the more substituted carbon.
Q2. Anti-Markovnikov addition of HBr to an alkene is promoted by:
A) Peroxides (ROOR) — radical mechanism
B) Strong acids only
C) Pd/C catalyst
D) Aqueous acid without initiator
Answer: A) Peroxides (ROOR)
Explanation: Peroxides initiate a radical chain mechanism (peroxide effect) that reverses regiochemistry so Br ends up on the less substituted carbon.
Q3. Hydroboration–oxidation of 1-butene yields which alcohol stereochemistry and regiochemistry?
A) Markovnikov, anti addition
B) Anti-Markovnikov, syn addition
C) Markovnikov, syn addition
D) Anti-Markovnikov, anti addition
Answer: B) Anti-Markovnikov, syn addition
Explanation: BH₃ adds syn across the double bond with boron attaching to the less substituted carbon; oxidation (H₂O₂/OH⁻) replaces B with OH, giving anti-Markovnikov alcohol.
Q4. Which reagent reliably converts an internal alkyne to a trans (E) alkene?
A) H₂ / Lindlar catalyst
B) Na / NH₃ (liquid ammonia)
C) HBr (excess)
D) H₂ / Pd (normal)
Answer: B) Na / NH₃ (liquid ammonia)
Explanation: Dissolving-metal reduction (Na/NH₃) adds H atoms in an anti manner, giving the trans (E) alkene. Lindlar gives cis (Z) alkene.
Q5. Ozonolysis of an alkene followed by reductive workup yields:
A) Alcohols only
B) Aldehydes and/or ketones (carbonyl compounds)
C) Only carboxylic acids under all conditions
D) No cleavage of C=C
Answer: B) Aldehydes and/or ketones (carbonyl compounds)
Explanation: Ozonolysis cleaves the C=C bond to carbonyl fragments. Reductive workup (e.g., Zn) yields aldehydes/ketones; oxidative conditions oxidize aldehydes further to acids.