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Chapter 11· Hydrocarbons
MCQs with Answers Try each one first: tap an option to check it, then read the reasoning and why the others are wrong.
A note about the questions
The wording follows published solved exercises and every answer was re-checked by hand, so the wording or the order of options may differ slightly from your print.
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Set A: Textbook exercise 10 MCQs The multiple-choice questions at the end of Chapter 11 in your book, in the book's option order.
Q11.1 Organic Compounds and Carbon
Which other atom is almost always present along with the carbon atom in all organic compounds?
(a) Oxygen (b) Nitrogen (c) Hydrogen (d) Halogen Show answer and reasoning Answer (c) Hydrogen
Step by step
C–H bonds are in almost every organic molecule. Why the others are wrong
(a) common, but absent in hydrocarbons.(b) only in some (amines, proteins).(d) only in alkyl halides.Remember
Organic = C and H.
Q11.2 Preparation of Alkanes
Which other metal can be used to reduce alkyl halides?
Show answer and reasoning Answer (b) Mg
Step by step
Mg + 2HCl → MgCl₂ + 2[H]. R–X + 2[H] → R–H + HX. Why the others are wrong
(a) aluminium is not used for this reduction (its oxide layer makes it slow).(c) nickel is the catalyst for adding H₂ to alkenes, not a reducing metal with acid.(d) cobalt is not used.Remember
A reactive metal that makes hydrogen with acid: Mg (like Zn).
Q11.3 Combustion and Uses
If naphtha undergoes a combustion reaction, what products do you expect it to form?
(a) Alkanes (b) Alkenes (c) CO₂ and H₂O (d) Both alkanes and alkenes Show answer and reasoning Answer (c) CO₂ and H₂O
Step by step
Combustion: hydrocarbon + O₂ → CO₂ + H₂O + heat. Why the others are wrong
(a) that is cracking.(b) that is cracking.(d) that is cracking.Remember
Burning = CO₂ + H₂O; cracking = smaller hydrocarbons.
Q11.4 Preparation of Alkanes
Why does a mixture of zinc and hydrochloric acid act as a reducing agent?
(a) Because zinc acts as a reducing agent. (b) Because atomic hydrogen is produced with Zn / HCl which acts as a reducing agent. (c) Because molecular hydrogen is produced with Zn / HCl which acts as a reducing agent. (d) Because chloride ions are produced with Zn / HCl which act as a reducing agent. Show answer and reasoning Answer (b) Because atomic hydrogen is produced with Zn / HCl which acts as a reducing agent.
Step by step
[H] = atomic (nascent) hydrogen, more reactive than H₂. Why the others are wrong
(a) not the book's reason, zinc is oxidised, but the alkyl halide is reduced by the hydrogen atoms formed.(c) ordinary H₂ gas does not reduce alkyl halides under these conditions.(d) chloride ions are not reducing agents here.Remember
Square brackets [H] = atomic hydrogen.
Q11.5 Combustion and Uses
Which alkane will evolve the most amount of heat when it is burnt with oxygen?
(a) Ethane (b) Propane (c) n-Butane (d) iso-Butane Show answer and reasoning Answer (c) n-Butane
Step by step
Ethane 1560, propane 2220, iso-butane 2869, n-butane 2877 kJ mol⁻¹. Why the others are wrong
(a) smallest of the four.(b) less than butane.(d) only slightly less than n-butane.Remember
More carbons = more heat; straight chain a little more than branched.
Q11.6 Halogenation of Alkanes
Which reaction is not given by alkanes?
(a) Substitution (b) Combustion (c) Addition (d) Cracking Show answer and reasoning Answer (c) Addition
Step by step
No double bond → no addition. Why the others are wrong
(a) they give it (chlorination).(b) they burn.(d) large alkanes crack.Remember
Saturated = full = no addition.
Q11.7 Combustion and Uses
Which hydrocarbon is responsible for explosions in coal mines?
(a) Butane (b) Pentane (c) Methane (d) Ethene Show answer and reasoning Answer (c) Methane
Step by step
CH₄ + 2O₂ → CO₂ + 2H₂O + heat, very fast in a mixture. Why the others are wrong
(a) Wrong.(b) a liquid.(d) Wrong.Remember
Mines and kitchens: methane.
Q11.8 Preparation of Alkanes
Which product will be formed when ethyl bromide (CH₃CH₂Br) is treated with Zn/HCl?
(a) CH₄ (b) CH₃–CH₃ (c) CH₃–CH₂–CH₂–CH₃ (d) CH₃–CH₂–CH₃ Show answer and reasoning Answer (b) CH₃–CH₃
Step by step
R–X + 2[H] → R–H + HX. R = C₂H₅ → ethane. Why the others are wrong
(a) one carbon lost.(c) that would need joining two chains (not with Zn/HCl).(d) one carbon too many.Remember
Same number of carbons.
Q11.9 Halogenation of Alkanes
Which of the following is not a process of halogenation of alkanes?
(a) Cracking (b) Chlorination (c) Bromination (d) Iodination Show answer and reasoning Answer (a) Cracking
Step by step
Chlorination, bromination, iodination all add a halogen. Why the others are wrong
(b) it is halogenation.(c) it is halogenation.(d) it is halogenation (though slow).Remember
Cracking = breaking, not halogen.
Q11.10 Combustion and Uses
How many moles of oxygen will be required to completely burn propane?
(a) 4 moles (b) 5 moles (c) 3 moles (d) 6 moles Show answer and reasoning Answer (b) 5 moles
Step by step
3 C → 3 CO₂ (6 O). 8 H → 4 H₂O (4 O). 10 O atoms = 5 O₂. Why the others are wrong
(a) Wrong.(c) only enough for the carbon.(d) Wrong.Remember
O₂ = C + H/4 = 3 + 2.
Set B: More MCQs from this chapter 14 MCQs Extra questions on the same ideas, of the kind set in board papers and class tests.
QB1 Organic Compounds and Carbon
The self-linking property of carbon is called:
(a) isomerism (b) hydrogenation (c) cracking (d) catenation Show answer and reasoning Answer (d) catenation
Step by step
C–C–C–C... chains. Why the others are wrong
(a) Wrong.(b) Wrong.(c) Wrong.QB2 Organic Compounds and Carbon
Which of these is classified as an inorganic compound although it contains carbon?
(a) CaCO₃ (b) C₂H₆ (c) CH₄ (d) CH₃Cl Show answer and reasoning Answer (a) CaCO₃
Step by step
CaCO₃ is a carbonate → inorganic. Why the others are wrong
(b) organic.(c) organic.(d) organic (alkyl halide).Remember
Carbonates and carbon oxides are inorganic.
QB3 Organic Compounds and Carbon
Carbon forms how many covalent bonds?
Show answer and reasoning Answer (d) 4
Step by step
4 outer electrons → 4 bonds. Why the others are wrong
(a) Wrong.(b) Wrong.(c) Wrong.Remember
Carbon is tetravalent.
QB4 Hydrocarbons and Alkanes
The general formula of alkanes is:
(a) CₙH₂ₙ₊₂ (b) CₙH₂ₙ (c) CₙH₂ₙ₋₂ (d) CₙHₙ Show answer and reasoning Answer (a) CₙH₂ₙ₊₂
Step by step
n = 3: C₃H₈ (2×3 + 2 = 8). Why the others are wrong
(b) alkenes.(c) alkynes.(d) Wrong.Remember
Alkanes: double plus two.
QB5 Hydrocarbons and Alkanes
Alkanes are called saturated hydrocarbons because:
(a) they dissolve in water (b) they are gases (c) they contain double bonds (d) all four valencies of carbon are used in single bonds Show answer and reasoning Answer (d) all four valencies of carbon are used in single bonds
Step by step
Only C–C and C–H single bonds. Why the others are wrong
(a) they are insoluble.(b) many are liquids or solids.(c) that is unsaturated.Remember
Saturated = full of single bonds.
QB6 Hydrocarbons and Alkanes
Alkanes are also called paraffins, which means:
(a) little affinity (b) very reactive (c) oil forming (d) gas forming Show answer and reasoning Answer (a) little affinity
Step by step
Para + affinis = little affinity. Why the others are wrong
(b) Wrong.(c) Wrong.(d) Wrong.QB7 IUPAC Nomenclature
The IUPAC root for a chain of five carbon atoms is:
(a) But- (b) Prop- (c) Hex- (d) Pent- Show answer and reasoning Answer (d) Pent-
Step by step
5 → pent-. Why the others are wrong
Remember
Pentagon has 5 sides.
QB8 IUPAC Nomenclature
The IUPAC name of CH₃–CH(CH₃)–CH₂–CH₃ is:
(a) 3-methylbutane (b) 2-methylbutane (c) pentane (d) 2-methylpropane Show answer and reasoning Answer (b) 2-methylbutane
Step by step
Root but-, suffix -ane. Branch methyl on C-2. Why the others are wrong
(a) numbered from the wrong end.(c) pentane is unbranched.(d) that is isobutane (4 carbons).Remember
Number from the end closest to the branch.
QB9 Preparation of Alkanes
In catalytic cracking of naphtha, the catalyst used is:
(a) zeolite (b) nickel (c) platinum (d) iron Show answer and reasoning Answer (a) zeolite
Step by step
Naphtha → (500 °C, zeolite) C₅-C₁₀ alkanes + alkenes. Why the others are wrong
(b) hydrogenation.(c) Wrong.(d) Haber.Remember
Cracking catalyst: zeolite.
QB10 Preparation of Alkanes
Hydrogenation of ethene gives:
(a) methane (b) propane (c) ethyne (d) ethane Show answer and reasoning Answer (d) ethane
Step by step
Same carbons; double bond becomes single. Why the others are wrong
(a) methane cannot be made this way.(b) Wrong.(c) that has a triple bond.Remember
Add H₂ → -ene becomes -ane.
QB11 Preparation of Alkanes
Why can methane not be prepared by hydrogenation?
(a) It is too reactive (b) There is no alkene or alkyne with one carbon (c) Nickel does not work (d) Methane is a liquid Show answer and reasoning Answer (b) There is no alkene or alkyne with one carbon
Step by step
C=C needs two carbons. Why the others are wrong
(a) Wrong.(c) Wrong.(d) a gas.Remember
One carbon cannot have a C=C.
QB12 Halogenation of Alkanes
Chlorination of methane takes place in the presence of:
(a) UV light (sunlight) (b) darkness (c) water (d) nickel Show answer and reasoning Answer (a) UV light (sunlight)
Step by step
Light splits Cl₂ into reactive Cl atoms. Why the others are wrong
(b) no reaction in the dark.(c) Wrong.(d) Wrong.Remember
hν over the arrow = light.
QB13 Halogenation of Alkanes
The common name of trichloromethane (CHCl₃) is:
(a) carbon tetrachloride (b) methyl chloride (c) chloroform (d) dichloromethane Show answer and reasoning Answer (c) chloroform
Step by step
Three Cl → chloroform. Why the others are wrong
(a) CCl₄.(b) CH₃Cl.(d) CH₂Cl₂.Remember
Chloro-form: CHCl₃.
QB14 Halogenation of Alkanes
Alkanes are unreactive towards acids, bases and oxidising agents because:
(a) they are gases (b) they are ionic (c) they contain double bonds (d) their bonds are almost non-polar Show answer and reasoning Answer (d) their bonds are almost non-polar
Step by step
Small EN difference → non-polar → no attack points. Why the others are wrong
(a) Wrong.(b) covalent.(c) single bonds only.Remember
No charges, no handles.
