NEET (UG)

Practice Test 1 — Hydrocarbons

12 questions • 18 minutes • auto-graded with full solutions

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Section A — MCQ (Single Correct & Statement-based)

Question 1

The general formula of an alkene is:

Solution: One double bond: $\text{C}_n\text{H}_{2n}$.

Question 2

Addition of HBr to propene without peroxide gives mainly:

Solution: Markovnikov: 2-bromopropane.

Question 3

The peroxide effect occurs with:

Solution: Only HBr shows anti-Markovnikov peroxide effect.

Question 4

Statements: (I) Benzene has 6 delocalised pi electrons. (II) Benzene undergoes addition more readily than substitution. Which is/are correct?

Solution: I correct; II wrong — benzene prefers substitution.

Question 5

Decolourisation of bromine water by a compound indicates:

Solution: Test for unsaturation (C=C or C≡C).

Question 6

The electrophile in Friedel–Crafts acylation is:

Solution: Acylium ion $\text{RCO}^+$ with $\text{AlCl}_3$.

Question 7

A terminal alkyne can be identified using:

Solution: Forms a coloured acetylide precipitate.

Question 8

Which group is ortho/para-directing but deactivating?

Solution: Halogens are o/p-directing yet deactivating.

Section B — Assertion & Reason

Question 9

A: Addition of HBr to propene gives 2-bromopropane as the major product.
R: The reaction proceeds through the more stable secondary carbocation (Markovnikov's rule).

Solution: The more stable carbocation route gives 2-bromopropane — R explains A.

Question 10

A: Benzene undergoes substitution rather than addition reactions.
R: Substitution preserves the stable aromatic six-pi-electron system.

Solution: Keeping the aromatic system intact is exactly why substitution is favoured — R explains A.

Question 11

A: The nitro group directs an incoming electrophile to the ortho and para positions of benzene.
R: The nitro group is an electron-withdrawing group.

Solution: The nitro group is meta-directing (so A is false), and it is indeed electron-withdrawing (R true).

Question 12

A: Only HBr shows the peroxide (anti-Markovnikov) effect.
R: The peroxide effect proceeds by a free-radical chain mechanism that is energetically favourable only for HBr.

Solution: Only HBr's bond energies make the radical chain feasible — R explains A.