NEET ChemistryUpdated 19 Oct 2026

Hydrocarbons: NEET PYQs and weightage

Hydrocarbons carries 5.9 of 100 Chemistry marks in NEET by past-paper share: 42 of the 707 tagged NEET Chemistry PYQs in the ViJEEta bank (NEET 2013–2026). It ranks 3 of 26 Chemistry chapters.

Take the 25-question Hydrocarbons test Key facts ↓All NEET Chemistry chapters

5.9/100 Weight in Chemistry

Exam importance (4/5, by past-paper share)

42 NEET PYQs

505 Practice questions

453 With measured difficulty

How the weight is computed: this chapter's tagged NEET PYQs divided by all tagged NEET Chemistry PYQs in the bank (42 of 707), times 100, with repeated questions counted once. The bank does not store the year of each NEET question, so none is printed. Computed from the bank at build time. Updated 19 Oct 2026.

Hydrocarbons: key facts for NEET

16 facts the paper keeps asking, each with how it is asked. Copy it onto one page of your notebook: that page is this chapter's handbook.

Alkanes: formula and shape
Alkanes are $C_{n} H_{2n + 2}$ and $s p^{3}$ with a tetrahedral shape: $H - C - H$ is $109. 5^{\circ}$ , $C - C$ is $154 pm$ and $C - H$ is $112 pm$ .
Asked as: hybridisation or bond angle of methane, or which formula belongs to the alkane series.
Chain isomers of alkanes
Chain isomers: $C_{4} H_{10}$ has 2, $C_{5} H_{12}$ has 3, $C_{6} H_{14}$ has 5, $C_{7} H_{16}$ has 9, and $C_{10} H_{22}$ has 75.
Asked as: "How many structural isomers does $C_{6} H_{14}$ have?"
Preparation of alkanes
Wurtz ( $R - X + Na$ in dry ether) and Kolbe electrolysis (alkane forms at the anode) both give even-carbon alkanes. Soda-lime decarboxylation gives an alkane with one carbon less.
Asked as: methane cannot be made by Kolbe's method; the sodium salt of butanoic acid gives propane.
Physical state and boiling points
$C_{1}$ – $C_{4}$ are gases, $C_{5}$ – $C_{17}$ are liquids and $C_{18} +$ are solids. Branching lowers b.p.: n-pentane $309 K >$ isopentane $301 K >$ neopentane $282.5 K$ .
Asked as: arrange isomeric pentanes by boiling point (a more spherical shape means less surface contact).
Halogenation of alkanes
Halogenation is free radical (needs $h ν$ or heat). Halogen reactivity is $F_{2} > C l_{2} > B r_{2} > I_{2}$ , and H replacement is $3^{\circ} > 2^{\circ} > 1^{\circ}$ . Iodination is reversible and needs $HI O_{3}$ or $HN O_{3}$ .
Asked as: why ethane forms during chlorination of methane (two $C H_{3}^{∙}$ radicals combine at termination).
Conformations of ethane
Staggered ethane is more stable than eclipsed ethane, with an energy gap of about $12.5 kJ mo l^{- 1}$ . Bond angles and lengths stay the same, and the conformers cannot be isolated.
Asked as: which conformation has maximum torsional strain, or the size of the energy barrier.
Alkenes: the double bond
Alkenes are $C_{n} H_{2n}$ . $C = C$ is one $s p^{2}$ $σ$ bond ( $\sim 397 kJ mo l^{- 1}$ ) plus one weaker $π$ bond ( $\sim 284 kJ mo l^{- 1}$ ). $C = C$ is $681 kJ mo l^{- 1}$ against $348$ for $C - C$ .
Asked as: why alkenes are attacked by electrophiles (loosely held $π$ electrons).
Cis-trans isomerism
Cis-trans isomerism needs two different groups on each doubly bonded carbon. Cis-but-2-ene has $μ = 0.33 D$ and trans has $μ \approx 0$ , but the trans isomer has the higher m.p.
Asked as: which compound shows geometrical isomerism; $C H_{2} = CB r_{2}$ does not.
Preparation of alkenes
Lindlar's catalyst ( $Pd/C$ poisoned with sulphur compounds or quinoline) gives cis alkenes and Na in liquid $N H_{3}$ gives trans alkenes. Alcoholic KOH removes HX by $β$ -elimination, with rate $I > Br > Cl$ for the halogen and $3^{\circ} > 2^{\circ} > 1^{\circ}$ for the alkyl group.
Asked as: match the reagent to the geometry of the product, or which alkyl halide dehydrohalogenates fastest.
Markovnikov rule
Markovnikov rule: the negative part adds to the carbon with fewer H atoms, via the more stable carbocation (for propene, the $2^{\circ}$ carbocation rather than the $1^{\circ}$ ). Propene + HBr gives 2-bromopropane. HX reactivity is $HI > HBr > HCl$ .
Asked as: the major product of HX adding to an unsymmetrical alkene.
Peroxide (Kharash) effect
The peroxide (Kharash) effect gives anti-Markovnikov addition by a free radical path. Propene + HBr + benzoyl peroxide gives 1-bromopropane.
Asked as: "Peroxide effect is shown by: HCl / HBr / HI?"
Tests for unsaturation and ozonolysis
Two tests for unsaturation: reddish-orange $B r_{2}$ in $CC l_{4}$ is decolourised, and cold dilute aqueous $KMn O_{4}$ (Baeyer's reagent) gives vicinal glycols. Ozonolysis ( $O_{3}$ followed by $Zn - H_{2} O$ ) locates the double bond.
Asked as: identify the alkene from its ozonolysis products, e.g. ethanal + pentan-3-one.
Alkynes: the triple bond
Alkynes are $C_{n} H_{2n - 2}$ . Ethyne is $s p$ -hybridised, linear ( $18 0^{\circ}$ ), with $C \equiv C$ at $120 pm$ and $823 kJ mo l^{- 1}$ , made of 1 $σ$ and 2 $π$ bonds. $Ca C_{2} + H_{2} O$ gives ethyne.
Asked as: arrange $C - C$ , $C = C$ and $C \equiv C$ by bond length or bond enthalpy.
Acidity of terminal alkynes
Terminal alkyne H atoms are acidic because $s p$ carbon has $50%$ s character, so they react with Na or $NaN H_{2}$ . Acidity runs $HC \equiv CH > C H_{3} C \equiv CH ≫ C H_{3} C \equiv CC H_{3}$ , and ethyne $>$ ethene $>$ ethane.
Asked as: which alkyne does not form a sodium salt (but-2-yne).
Benzene and aromaticity
In benzene all $C - C$ bonds are $139 pm$ , between single ( $154 pm$ ) and double ( $133 pm$ ). The ring is planar and $s p^{2}$ , with 6 delocalised $π$ electrons. Aromaticity needs planarity, complete delocalisation and $(4 n + 2) π$ electrons (Hückel).
Asked as: which ring is aromatic, or why benzene prefers substitution to addition.
Directive influence of substituents
Directive influence: $- OH$ , $- N H_{2}$ , $- OC H_{3}$ and $- C H_{3}$ are o/p-directing and activating. Halogens are o/p-directing but deactivating. $- N O_{2}$ , $- CN$ , $- CHO$ , $- COOH$ and $- S O_{3} H$ are meta-directing.
Asked as: rank substituted benzenes by reactivity toward $E^{+}$ (toluene $>$ benzene $>$ m-dinitrobenzene).

Trap

The peroxide effect works only with HBr. With HCl, the H–Cl bond (430.5 kJ mol⁻¹) is too strong for the free radical to break. With HI, iodine radicals join to form I₂ instead of adding to the double bond. So HCl and HI always follow Markovnikov, even when peroxide is present.

How does NEET ask Hydrocarbons?

8 real previous-year questions from this chapter, as printed in the paper, each with its worked solution. Answer the first one here with no sign-in.

Q1ChemistryNEET UG PYQPreparation of Alkanes

Try right here · No sign-in

Which of the following alkane cannot be made in good yield by Wurtz reaction?

Answer key (A) & worked solution

Correct answer: Option A

Wurtz reaction is used to prepare symmetrical alkane.

Q2ChemistryNEET UG PYQPreparation of Alkanes

Hydrocarbon (A) reacts with bromine by substitution to form an alkyl bromide which by Wurtz reaction is converted to gaseous hydrocarbon containing less than four carbon atoms. (A) is

ACH

_{3}

– CH

_{3}

BCH

_{2}

= CH

_{2}

CCH ≡ CH

DCH

_{4}

Answer key (D) & worked solution

Correct answer: Option D

C H_{4} B r_{2} / h v C H_{3} B r Na/dry ether wurtzreaction C H_{3} - C H_{3}

Hence the correct option is (4)

Q3ChemistryNEET UG PYQChemical Properties of Alkenes

Which of the following statements are NOT correct? A. Hydrogen is used to reduce heavy metal oxides to metals. B. Heavy water is used to study reaction mechanism. C. Hydrogen is used to make saturated fats from oils D. The

H - H

bond dissociation enthalpy is lowest as compared to a single bond between two atoms of any element. E. Hydrogen reduces oxides of metals that are more active than iron. Choose the most appropriate answer from the options given below:

AB, D only

BD, E only

CA, B, C only

DB, C, D, E only

Answer key (B) & worked solution

Correct answer: Option B

(D, E) explanation (D)

H - H

bond strength/ bond dissociation energy/bond energy of

H_{2}

can not be lowest because bond formed between hydrogen atoms is due to overlapping of

1 s - 1 s

. (E) Hydrogen can not reduces oxides of highly reactive metal.

Q4ChemistryNEET UG PYQChemical Properties of Alkanes

Methane reacts with steam at 1273 K in the presence of nickel catalyst to form :

ACO and

H_{2}

BCO and

H_{2} O

CO_{2}

and

H_{2} O

CO_{2}

and

H_{2}

Answer key (A) & worked solution

Correct answer: Option A

C H_{4} (g) + H_{2} O (g) Ni Δ, (1273 K) CO + 3 H_{2}

(Used for industrial preparation of dihydrogen gas)

Q5ChemistryNEET UG PYQChemical Properties of Aromatic Hydrocarbons

Which of the following compounds will not undergo Friedal-Craft’s reaction easily?

ACumene

BXylene

CNitrobenzene

DToluene

Answer key (C) & worked solution

Correct answer: Option C

-NO

_{2}

is a deactivating group, and therefore, nitrobenzene will not undergo Friedal-Crafts reaction.

Q6ChemistryNEET UG PYQChemical Properties of Alkynes

Which one is the correct order of acidity?

ACH

\equiv

CH > CH

_{2}

= CH

_{2}

> CH

_{3}

– C

\equiv

CH > CH

_{3}

– CH

_{3}

BCH

_{3}

– CH

_{3}

> CH

_{2}

= CH

_{2}

> CH

_{3}

– C

\equiv

CH > CH

\equiv

CCH

_{2}

= CH

_{2}

_{3}

– C

\equiv

CH > CH

\equiv

DCH

\equiv

CH > CH

_{3}

– C

\equiv

CH > CH

_{2}

= CH

_{2}

> CH

_{3}

– CH

_{3}

Answer key (D) & worked solution

Correct answer: Option D

Correct order is

(Two acidic hydrogens) H - C \equiv C - H (One acidic hydrogen) > H_{3} C - C - H > H_{2} C = C H_{2} > C H_{3} - C H_{3}

Q7ChemistryNEET UG PYQPhysical Properties of Alkanes

Given below are two statements: Statement I: The boiling point of three isomeric pentanes follows the order n-pentane > isopentane > neopentane Statement II: When branching increases, the molecule attains a shape of sphere. This results in smaller surface area for contact, due to which the intermolecular forces between the spherical molecules are weak, thereby lowering the boiling point. In the light of the above statements, choose the most appropriate answer from the options given below:

ABoth statement I and statement II are incorrect

BStatement I is correct but statement II is incorrect

CStatement I is incorrect but statement II is correct

DBoth statement I and statement II are correct

Answer key (D) & worked solution

Correct answer: Option D

Boiling point \propto \frac{1}{B r an c hin g}

Branching increases boiling point decreases Pentane, 309.1 K Isopentane, 300.9 K Neopentane, 282.9 K Option (d) is correct

Q8ChemistryNEET UG PYQChemical Properties of Aromatic Hydrocarbons

Some meta-direction substituents in aromatic substitution are given. Which one is most deactivating ?

- C \equiv N

B–SO

_{3}

C-COOH

D–NO

_{2}

Answer key (D) & worked solution

Correct answer: Option D

-NO

_{2}

is the most deactivating.

Which topics in Hydrocarbons carry the most questions?

The 12 busiest of 26 topics, by tagged PYQs, then practice questions. Counted from the bank. Updated 19 Oct 2026.

Topic	PYQs	Practice questions
Chemical Properties of Alkenes	15	163
Chemical Properties of Aromatic Hydrocarbons	10	98
Chemical Properties of Alkynes	4	46
Preparation of Alkanes	4	30
Chemical Properties of Alkanes	2	40
Preparation of Alkynes	1	13
Physical Properties of Alkanes	1	11
Introduction and Classification of Hydrocarbons	1	9
Nomenclature of Hydrocarbons	1	8
Preparation of Aromatic Hydrocarbons	1	7
Structure of Alkenes	1	6
Isomerism in Alkenes	1	5

Why does Hydrocarbons show "–" until you answer 3 questions?

Unknown is not zero. Until you answer at least 3 graded questions in Hydrocarbons, ViJEEta shows – instead of a zero or a 50% default. Book exercises can raise chapter mastery up to 0.60, adaptive practice up to 0.75, and only a timed chapter test or mock can certify 0.80 and above.

How ViJEEta scores you

What happens when you test Hydrocarbons?

Every chapter test is 25 questions. It starts at moderate difficulty and adapts after each saved answer. If you open a solution before answering, that attempt earns no credit, so your mastery stays honest.

Start the Hydrocarbons test

Chapters either side of Hydrocarbons by weight

Chemical Bonding and Molecular Structure Weight 9.2/100 Coordination Compounds Weight 6.5/100 Solutions Weight 5.7/100 Alcohols, Phenols, and Ethers Weight 5.0/100

Hydrocarbons: NEET PYQs and weightage

Hydrocarbons: key facts for NEET

Alkanes: formula and shape

Chain isomers of alkanes

Preparation of alkanes

Physical state and boiling points

Halogenation of alkanes

Conformations of ethane

Alkenes: the double bond

Cis-trans isomerism

Preparation of alkenes

Markovnikov rule

Peroxide (Kharash) effect

Tests for unsaturation and ozonolysis

Alkynes: the triple bond

Acidity of terminal alkynes

Benzene and aromaticity

Directive influence of substituents

How does NEET ask Hydrocarbons?

Which topics in Hydrocarbons carry the most questions?

Why does Hydrocarbons show "–" until you answer 3 questions?

What happens when you test Hydrocarbons?

Chapters either side of Hydrocarbons by weight