PIEAS Entry Test Chemistry: Organic Chemistry MCQs

PIEAS Entry Test Chemistry: Organic Chemistry MCQs — sample questions

1. Question 1

   Q1. The hybridization of carbon in CH4 is

   • A) sp
   • B) sp²
   • C) sp³
   • D) dsp²

   Answer: sp³

   Explanation: Carbon in CH4 is bonded to four atoms, requiring sp³ hybridization for tetrahedral geometry.

2. Question 2

   Q2. The most stable conformation of n-butane is

   • A) Eclipsed
   • B) Staggered
   • C) Gauche
   • D) Anti

   Answer: Anti

   Explanation: Anti conformation is most stable due to least steric hindrance between bulky groups.

3. Question 3

   Q3. The reaction of alkyl halide with NaI in acetone is an example of

   • A) SN1
   • B) SN2
   • C) E1
   • D) E2

   Answer: SN2

   Explanation: NaI in acetone favors SN2 due to strong nucleophile and polar aprotic solvent.

4. Question 4

   Q4. The compound with the highest boiling point among the following is

   • A) CH₃CH₂CH₃
   • B) CH₃CH₂OH
   • C) CH₃OCH₃
   • D) CH₃CHO

   Answer: CH₃CH₂OH

   Explanation: Hydrogen bonding in CH₃CH₂OH increases its boiling point.

5. Question 5

   Q5. The IUPAC name of (CH₃)₃CCH₂CH₃ is

   • A) 2,2-Dimethylbutane
   • B) 2,2,2-Trimethylbutane
   • C) 3,3-Dimethylpentane
   • D) 2,2-Dimethylpentane

   Answer: 2,2-Dimethylpentane

   Explanation: Longest chain has 5 carbons; two methyl groups are on C-2.

6. Question 6

   Q6. The major product of dehydration of 2-methyl-2-butanol is

   • A) 2-Methyl-1-butene
   • B) 2-Methyl-2-butene
   • C) 3-Methyl-1-butene
   • D) 3-Methyl-2-butene

   Answer: 2-Methyl-2-butene

   Explanation: Most stable alkene (more substituted) is formed according to Zaitsev's rule.

7. Question 7

   Q7. Which of the following is a chiral molecule?

   • A) CH₃CH₂CH₂CH₃
   • B) CH₃CH₂CH(CH₃)₂
   • C) CH₃CH(CH₃)CH₂CH₃
   • D) CH₃CH₂CH₂OH

   Answer: CH₃CH(CH₃)CH₂CH₃

   Explanation: Presence of a stereocenter (asymmetric carbon) makes the molecule chiral.

8. Question 8

   Q8. The order of reactivity of alkyl halides towards SN2 reaction is

   • A) 3° > 2° > 1°
   • B) 1° > 2° > 3°
   • C) 2° > 1° > 3°
   • D) 3° > 1° > 2°

   Answer: 1° > 2° > 3°

   Explanation: SN2 reactivity decreases with increasing steric hindrance around the reaction center.

9. Question 9

   Q9. The compound that will not give iodoform test is

   • A) CH₃CH₂OH
   • B) CH₃CHO
   • C) CH₃CH(OH)CH₃
   • D) (CH₃)₃COH

   Answer: (CH₃)₃COH

   Explanation: Iodoform test requires a methyl group attached to the carbonyl or a secondary alcohol with a methyl group.

10. Question 10

    Q10. The reaction of Grignard reagent with CO2 gives

    • A) Alcohol
    • B) Ketone
    • C) Carboxylic acid
    • D) Aldehyde

    Answer: Carboxylic acid

    Explanation: Grignard reagent adds to CO2 to form a carboxylate, which upon acidification gives a carboxylic acid.

11. Question 11

    Q11. The most acidic compound among the following is

    • A) CH₃COOH
    • B) CCl₃COOH
    • C) HCOOH
    • D) ClCH₂COOH

    Answer: CCl₃COOH

    Explanation: Electron-withdrawing groups (like Cl) increase acidity; three Cl atoms make CCl₃COOH most acidic.

12. Question 12

    Q12. The compound that will undergo Friedel-Crafts alkylation is

    • A) Benzene
    • B) Nitrobenzene
    • C) Chlorobenzene
    • D) Aniline

    Answer: Benzene

    Explanation: Benzene is most reactive towards Friedel-Crafts alkylation due to its high electron density.

13. Question 13

    Q13. The reaction of benzene with Cl2 in presence of AlCl3 is

    • A) Electrophilic substitution
    • B) Nucleophilic substitution
    • C) Electrophilic addition
    • D) Nucleophilic addition

    Answer: Electrophilic substitution

    Explanation: AlCl3 catalyzes the formation of Cl⁺ electrophile, which substitutes onto the benzene ring.

14. Question 14

    Q14. The compound with the formula C4H8O that gives a positive Tollens' test is

    • A) Butanal
    • B) 2-Butanone
    • C) Butan-2-ol
    • D) Tetrahydrofuran

    Answer: Butanal

    Explanation: Tollens' test is positive for aldehydes, which have a reducible carbonyl group.

15. Question 15

    Q15. The best leaving group among the following halides is

    • A) F⁻
    • B) Cl⁻
    • C) Br⁻
    • D) I⁻

    Answer: I⁻

    Explanation: I⁻ is the best leaving group due to its weak basicity and good ability to stabilize the negative charge.

16. Question 16

    Q16. The reaction that involves the formation of a carbocation is

    • A) SN2
    • B) SN1
    • C) E2
    • D) E1cB

    Answer: SN1

    Explanation: SN1 involves the formation of a carbocation intermediate before nucleophilic attack.

17. Question 17

    Q17. The compound that will not react with Na is

    • A) CH₃OH
    • B) C2H5OH
    • C) H2O
    • D) C6H5OH

    Answer: C6H5OH

    Explanation: Phenol reacts very slowly with Na compared to alcohols and water.

18. Question 18

    Q18. The hybridization of the carbon atom in CO2 is

    • A) sp
    • B) sp²
    • C) sp³
    • D) dsp²

    Answer: sp

    Explanation: CO2 has a linear geometry, indicating sp hybridization on the carbon atom.

19. Question 19

    Q19. The functional group in CH₃COCH₃ is

    • A) Aldehyde
    • B) Ketone
    • C) Carboxylic acid
    • D) Ester

    Answer: Ketone

    Explanation: The carbonyl group (C=O) bonded to two alkyl groups is characteristic of a ketone.

20. Question 20

    Q20. The compound that can exhibit tautomerism is

    • A) CH₃CHO
    • B) CH₃COCH₃
    • C) CH₃COCH2COCH₃
    • D) C6H5CHO

    Answer: CH₃COCH2COCH₃

    Explanation: Tautomerism occurs in compounds with a hydrogen atom that can migrate to a nearby carbonyl group, as in β-diketones.