20 challenging multiple-choice organic chemistry questions, each followed by a detailed step-by-step solution for the correct option:

**Question 1:** Which of the following is the correct IUPAC name for the compound CH₃CH₂C≡CH?

a) 1-Ethynylbutane

b) 2-Ethyl-1-butyne

c) 1-Butyl-2-ethyne

d) 1-Buten-3-yne

**Solution:** The correct IUPAC name is **b) 2-Ethyl-1-butyne.**

**Question 2:** Which of the following compounds is an example of an aldehyde?

a) Propanone

b) Butanal

c) Pentanone

d) Methanoic acid

**Solution:** The correct answer is **b) Butanal.**

**Question 3:** When ethanol (C₂H₅OH) is oxidized, which functional group is converted into another functional group?

a) Alcohol to ketone

b) Alcohol to aldehyde

c) Alcohol to carboxylic acid

d) Alcohol to ether

**Solution:** The correct answer is **c) Alcohol to carboxylic acid.**

**Question 4:** Which of the following reagents is commonly used to convert an alkene into an alkane?

a) H₂SO₄

b) HBr

c) Hg(OAc)₂

d) LiAlH₄

**Solution:** The correct answer is **d) LiAlH₄.**

**Question 5:** Which of the following reactions is a nucleophilic substitution reaction?

a) E1 elimination

b) E2 elimination

c) SN1 substitution

d) SN2 substitution

**Solution:** The correct answer is **d) SN2 substitution.**

**Question 6:** What is the product of the following reaction?

CH₃CH₂OH + HBr → ?

a) CH₃CH₂Br

b) CH₃CHBrOH

c) CH₃CHOHBr

d) CH₃CH₂OH₂Br

**Solution:** The correct answer is **a) CH₃CH₂Br.**

**Question 7:** Which of the following functional groups is present in both an aldehyde and a ketone?

a) Hydroxyl

b) Carbonyl

c) Carboxyl

d) Ester

**Solution:** The correct answer is **b) Carbonyl.**

**Question 8:** In the Friedel-Crafts alkylation reaction, which of the following compounds can be used as an alkylating agent?

a) Chloroethane

b) Benzene

c) Toluene

d) Chlorobenzene

**Solution:** The correct answer is **a) Chloroethane.**

**Question 9:** Which of the following compounds exhibits cis-trans isomerism?

a) Butane

b) Cyclopropane

c) Ethene

d) 1,2-Dichloroethene

**Solution:** The correct answer is **d) 1,2-Dichloroethene.**

**Question 10:** What is the hybridization of the carbon atom in a triple bond of an alkyne?

a) sp

b) sp²

c) sp³

d) dsp²

**Solution:** The correct answer is **a) sp.**

**Question 11:** Which of the following reagents is used to convert a carboxylic acid into an ester?

a) LiAlH₄

b) H₂SO₄

c) PBr₃

d) SOCl₂

**Solution:** The correct answer is **d) SOCl₂.**

**Question 12:** What is the major product of the following reaction?

HBr + CH₃CH=CH₂ → ?

a) CH₃CHBrCH₂

b) CH₃CHBr₂

c) CH₃CH₂CH₂Br

d) CH₃CHBrCH₂Br

**Solution:** The correct answer is **a) CH₃CHBrCH₂.**

**Question 13:** In the reaction CH₃MgBr + CO₂, what type of compound is formed?

a) Alcohol

b) Ketone

c) Carboxylic acid

d) Aldehyde

**Solution:** The correct answer is **c) Carboxylic acid.**

**Question 14:** Which of the following is a common reaction intermediate in nucleophilic acyl substitution reactions?

a) Carbocation

b) Carbanion

c) Carboxylate ion

d) Tetrahedral intermediate

**Solution:** The correct answer is **d) Tetrahedral intermediate.**

**Question 15:** Which of the following reactions is used to convert an alkyl halide into an alcohol?

a) Hydrogenation

b) Hydrolysis

c) Halogenation

d) Dehydration

**Solution:** The correct answer is **b) Hydrolysis.**

**Question 16:** What is the major product of the following reaction?

CH₃CH₂OH + TsCl → ?

a) CH₃CH₂OTs

b) CH₃CH₂Cl

c) CH₃CH₂OTs₂

d) CH₃CH₂Ts

**Solution:** The correct answer is **a) CH₃CH₂OTs.**

**Question 17:** Which of the following is NOT a common method for synthesizing alcohols?

a) Hydroboration

b) Grignard reaction

c) Dehydration

d) Reduction of a ketone

**Solution:** The correct answer is **c) Dehydration.**

**Question 18:** In the Fischer esterification reaction, what is the role of the acid catalyst?

a) It acts as a reducing agent.

b) It promotes elimination reactions.

c) It increases the rate of the reaction by protonating the carbonyl oxygen.

d) It acts as a nucleophile.

**Solution:** The correct answer is **c) It increases the rate of the reaction by protonating the carbonyl oxygen.**

**Question 19:** Which of the following is a common method for reducing a carboxylic acid to an alcohol?

a) Grignard reaction

b) Hydroboration

c) LiAlH₄ reduction

d) Friedel-Crafts reaction

**Solution:** The correct answer is **c) LiAlH₄ reduction.**

**Question 20:** In the reaction between an alkene and H₂ in the presence of a metal catalyst, what type of reaction occurs?

a) Electrophilic addition

b) Nucleophilic substitution

c) Elimination

d) Radical reaction

**Solution:** The correct answer is **a) Electrophilic addition.**

These challenging organic chemistry questions cover a wide range of topics, and the detailed step-by-step solutions for each correct option provide clarity and understanding of the concepts involved.