Practise 25 real Federal Board questions on Hydrocarbons from 2023 to 2026. See the answer and explanation as soon as you answer.
Hydrocarbons is one of the 19 main chapters in our Federal Board FSC Chemistry question bank (11th and 12th class), and about 5% of its real questions come from it. Tayyari Karo has 25 real questions on this chapter from 2023 to 2026; 9 are multiple choice and marked instantly, and the rest are short and long questions with a model answer. By difficulty: 14 medium, 7 hard, 4 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
These are real past-paper questions. Think of your answer first, then open the explanation.
Which of the following is a type of stereoisomerism?
Answer: C. Geometrical isomerism
Geometrical (cis-trans) isomerism is a type of stereoisomerism (same connectivity, different spatial arrangement); the others are structural isomerism types.
In the oxidation reactions side chain of alkyl benzene is converted into:
Answer: A. -COOH group
Strong oxidation (e.g. hot KMnO₄) of an alkylbenzene side chain, regardless of chain length, converts it to a -COOH (carboxylic acid) group directly on the ring.
Which reaction mechanism is involved in chlorination of methane in the presence of sunlight?
Answer: A. Free radical substitution
CH₄ + Cl₂ under sunlight proceeds via a free-radical chain substitution mechanism.
Which of the following alkyne would NOT yield a ketone on hydration reaction?
Answer: B. Acetylene
Markovnikov hydration of alkynes gives ketones, except for acetylene (HC≡CH) itself, which gives acetaldehyde — an aldehyde, not a ketone.
Which of the following compounds will NOT show geometrical isomerism?
Answer: B. 1-Butene
1-Butene (CH₂=CH–CH₂–CH₃) has two identical H atoms on one double-bond carbon, so it cannot show cis/trans isomerism, unlike 2-butene or the isomeric butenedioic acids (maleic/fumaric).
Ozonolysis of Ethene gives:
Answer: B. Methanal
Ozonolysis cleaves the C=C bond of ethene (CH₂=CH₂) to give two molecules of methanal (formaldehyde, HCHO).
Compare the enthalpy of hydrogenation of benzene and 1,3,5-cyclohexatriene and explain the significance of the difference.
The hypothetical 1,3,5-cyclohexatriene (a Kekulé structure with three isolated/localized double bonds) would have a calculated enthalpy of hydrogenation of about −360 kJ/mol (3× a single alkene's ~−120 kJ/mol), whereas real benzene's experimental enthalpy of hydrogenation is only about −208 kJ/mol (much less exothermic). This ~152 kJ/mol difference is the resonance/delocalization energy of benzene — it shows benzene's actual structure (with delocalized π-electrons) is significantly more stable than the hypothetical localized triene structure.
Draw the structure of given. a. 1,2-Dimethyl cyclo butane b. 1,3-Diethyl cyclo pentane
a. 1,2-Dimethylcyclobutane: a four-membered ring (cyclobutane) with a -CH₃ group attached to each of two adjacent ring carbons (C1 and C2).
b. 1,3-Diethylcyclopentane: a five-membered ring (cyclopentane) with a -C₂H₅ (ethyl) group attached to ring carbons C1 and C3 (separated by one carbon).
| Session | Questions |
|---|---|
| 2026 Annual | 6 |
| 2025 1st Annual | 5 |
| 2025 2nd Annual | 6 |
| 2024 Annual | 5 |
| 2023 Annual | 3 |
25 real Federal Board (FBISE) Chemistry questions on Hydrocarbons from 2023 to 2026, for 11th and 12th class. Each one shows the session it came from.
No. We could not find an official FBISE marking scheme for these papers, so the answers and explanations are written by Tayyari Karo for practice. Check anything important with your teacher or textbook.
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