39 practice MCQs on alkanes, alkenes, alkynes, benzene and aromatic compounds, and their characteristic reactions. Every question has the correct answer and an explanation.
Start free — 20 questionsHydrocarbons is part of the MDCAT Chemistry syllabus. This page collects Hydrocarbons MCQs in the style of past MDCAT papers — below are 12 of them with answers and explanations, and the full set of 39 questions is in the HighYield MDCAT QBank.
This chapter covers: alkanes, alkenes, alkynes, benzene and aromatic compounds, and their characteristic reactions.
Correct answer: C. Position isomerism
1-chloropropane and 2-chloropropane differ only in the position of the chlorine substituent on the same carbon skeleton, making them positional isomers.
Correct answer: A. Acetyl chloride
Benzene reacts with acetyl chloride in the presence of AlCl3 (Friedel-Crafts acylation) to produce acetophenone.
Correct answer: B. R-Cl
Friedel-Crafts alkylation introduces an alkyl group into benzene using an alkyl halide (R-Cl) in the presence of the AlCl3 catalyst.
Correct answer: B. CH₄ + 2O₂ → CO₂ + 2H₂O
CH4 + 2O2 to CO2 + 2H2O represents the complete combustion of methane, a saturated hydrocarbon, producing carbon dioxide and water.
Correct answer: D. Methyl Ketone group (CH₃-CO-R)
A methyl ketone group (CH3-CO-R) gives a positive iodoform test, forming a yellow precipitate of triiodomethane when warmed with alkaline aqueous iodine.
Correct answer: D. Elimination
The highly stable, delocalized electrons of benzene ring are not readily available for the nucleophillic attack like the electrons of alkenes. Therefore, the electrons of benzene ring do not assist in the attack of weak electrophiles. It means that more powerful electrophiles are required to penetrate and break the continuous sheath of electron cloud in benzene.Hence benzene undergoes electrophilic substitution. It is also oxidised in the presence of strong oxidising agent. It shows addition reaction in presence of appropriate catalyst.Benzene does not show any sort of elimination reaction.
Correct answer: B. Propagation step
In the chlorination of methane, the attack of a chlorine free radical on methane to form a methyl free radical occurs in the propagation step.
Correct answer: B. 2-bromobutane
The addition of HBr to 2-butene forms 2-bromobutane. Since it's a symmetrical alkene, it does not follow Markonivkov rules.
Correct answer: C. -NH2
This group is an electron-donating group due to its ability to donate a lone pair of electrons to the benzene ring, increasing the electron density of the ring and activating it toward electrophilic substitution reactions.
Correct answer: A. Clemmensen reduction
Clemmensen reduction is a chemical reaction described as a reduction of ketones or aldehydes to alkanes using zinc amalgam and concentrated hydrochloric acid.
Correct answer: A. NO2
A ring deactivator is a substituent that reduces the reactivity of the benzene ring towards electrophilic substitution reactions. NO2 (nitro group) is a strong ring deactivator because it:- Withdraws electrons from the ring through resonance- Has a negative inductive effect, reducing the electron density in the ring
Correct answer: B. Lesser number of hydrogen atoms
This is based on Markovnikov's Rule, which states that in the addition of a protic acid (such as HCl, HBr, etc.) to an unsymmetrical alkene, the hydrogen atom (the positive part of the reagent) attaches to the carbon with the greater number of hydrogen atoms, and the negative part (such as Cl⁻, Br⁻, etc.) attaches to the carbon with the fewer hydrogen atoms.
Start with 20 free questions — no card required. Unlock the full MDCAT QBank for chapter-wise drilling, timed tests and mock exams.