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NEET Hydrocarbons: 5 practice MCQs with answers

By the PrepMatic team · Updated 9 Oct 2026 · 3 min read

Hydrocarbons is the first reaction-heavy chapter in organic chemistry: alkanes, alkenes, alkynes and benzene, with their addition and substitution reactions. The five MCQs below test Markovnikov's rule, a test for terminal alkynes, ozonolysis, the nitrating electrophile and directing effects, at NCERT Class 11 level.

What this chapter covers in the NEET syllabus

Hydrocarbons is an NMC unit, matching the NCERT Class 11 chapter of the same name. The topics are:

• Classification of hydrocarbons, nomenclature and isomerism.
• Alkanes: physical properties, conformations of ethane, and halogenation by a free radical mechanism, combustion and pyrolysis.
• Alkenes: structure of the double bond, geometrical isomerism, and addition of hydrogen, halogens, water and hydrogen halides (Markovnikov's rule and the peroxide effect), ozonolysis and oxidation.
• Alkynes: structure of the triple bond, acidic character, and addition reactions.
• Aromatic hydrocarbons: benzene, resonance and aromaticity, and electrophilic substitution (nitration, sulphonation, halogenation, Friedel-Crafts), with the directive influence of substituents.

Five practice MCQs on Hydrocarbons

Question 1

Propene reacts with HBr in the absence of peroxide to give mainly:

• A. 1-bromopropane
• B. 2-bromopropane
• C. 1,2-dibromopropane
• D. propane

Question 2

Which of the following gives a white precipitate with ammoniacal silver nitrate solution?

• A. Propyne
• B. Ethene
• C. Propene
• D. 2-Butyne

Question 3

Reductive ozonolysis of propene, CH₃CH=CH₂, gives:

• A. acetone and formaldehyde
• B. acetaldehyde and formaldehyde
• C. two molecules of acetaldehyde
• D. propanal and methanol

Question 4

In the nitration of benzene with a mixture of concentrated HNO₃ and concentrated H₂SO₄, the attacking electrophile is:

• A. NO₂⁻
• B. NO
• C. HNO₂
• D. NO₂⁺

Question 5

Which of the following groups is meta-directing in electrophilic aromatic substitution?

• A. -OH
• B. -CH₃
• C. -NO₂
• D. -Cl

Answers and explanations

1. B. By Markovnikov's rule, the hydrogen of HBr adds to the carbon with more hydrogens, and bromine goes to the carbon with fewer, giving the more stable secondary carbocation. So the product is 2-bromopropane, CH₃CHBrCH₃. In the presence of peroxide, the addition reverses (anti-Markovnikov) and 1-bromopropane forms.
2. A. Propyne, CH₃-C≡CH, has an acidic hydrogen on the terminal sp carbon, so it forms a white silver salt with ammoniacal AgNO₃. Ethene and propene have no such hydrogen, and 2-butyne is an internal alkyne.
3. B. Ozonolysis cuts the C=C bond and puts a C=O on each carbon. The CH₃CH= end gives acetaldehyde (CH₃CHO) and the =CH₂ end gives formaldehyde (HCHO). Propene has one methyl-substituted carbon and one CH₂, so the two products are different.
4. D. The two acids react to produce the nitronium ion: HNO₃ + 2H₂SO₄ → NO₂⁺ + H₃O⁺ + 2HSO₄⁻. NO₂⁺ is a strong electrophile and attacks the benzene ring.
5. C. The nitro group withdraws electrons by both the −I and −M effects and deactivates the ring, directing the incoming group to the meta position. -OH and -CH₃ are ortho/para directing and activating. -Cl is also ortho/para directing, though it deactivates the ring.

How to prepare Hydrocarbons

• Learn the reactions as families, with the mechanism. Alkanes: free radical substitution. Alkenes and alkynes: electrophilic addition. Benzene: electrophilic substitution. Knowing the mechanism lets you predict the product when the reagent is new.
• Apply the rules in order. Markovnikov's rule (more stable carbocation) for HX addition, the peroxide effect for HBr only, and the directing effect for ring substitution. Be precise about the conditions.
• Draw the products of ozonolysis and oxidation. A frequent task is to work backwards: from the carbonyl products identify the alkene.
• Practise the conversions on paper. Alkyne to alkene (Lindlar's catalyst gives cis, Na/liquid NH₃ gives trans), alkene to alkane, benzene to toluene, nitrobenzene and chlorobenzene.
• Compare physical properties and stability. Boiling points rise with chain length and fall with branching. For aromaticity use Hückel's rule: a planar, cyclic, fully conjugated ring with (4n + 2) pi electrons.

Make a one-page reaction map of the chapter and revise it twice a week. The NEET organic chemistry guide covers the overall method, and the NEET Chemistry preparation guide places organic chemistry in your plan.

Take a full Hydrocarbons test on PrepMatic

Once your reaction map is ready, take a timed topic test on PrepMatic (about 15 questions in 30 minutes) and see the score with NEET's negative marking. The free Basic plan includes topic tests, and the practice hub lists related chapters.

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