Shifa International Entry Test Chemistry: Organic Chemistry Basics MCQs

Practice Organic Chemistry Basics MCQs for Shifa International Entry Test Chemistry — topic-wise sets with solved answers.

Shifa International Entry Test Chemistry: Organic Chemistry Basics MCQs — sample questions

  1. Question 1

    Q1. A 0.44 g sample of an organic compound containing only carbon, hydrogen, and oxygen is burnt, yielding 0.88 g of CO2. What is the percentage of carbon?

    • A) 54.54%
    • B) 27.27%
    • C) 12.00%
    • D) 44.00%

    Answer: 54.54%

    Explanation: Calculation uses mass of CO2 and sample. 27.27% is wrong because it ignores the 12/44 ratio of carbon in CO2.

  2. Question 2

    Q2. A chemist analyzes a hydrocarbon and finds it contains 85.7% carbon and 14.3% hydrogen by mass. What is its empirical formula?

    • A) CH
    • B) CH2
    • C) C2H4
    • D) CH4

    Answer: CH2

    Explanation: Atomic ratios are 1:2. C2H4 is the molecular formula, not the empirical formula which must be the simplest ratio.

  3. Question 3

    Q3. During a laboratory experiment, a student synthesizes an alkane with a molecular mass of 72 amu. How many structural isomers can this alkane form?

    • A) 1
    • B) 2
    • C) 3
    • D) 5

    Answer: 3

    Explanation: Pentane (C5H12) has mass 72 and forms three isomers; 2 is wrong as it ignores the branched neopentane structure.

  4. Question 4

    Q4. A fuel sample is prepared by mixing 70% iso-octane and 30% n-heptane by volume. What is the octane number assigned to this specific fuel blend?

    • A) 100
    • B) 0
    • C) 30
    • D) 70

    Answer: 70

    Explanation: Octane number equals the percentage of iso-octane. 30 is wrong because it represents the n-heptane percentage, not the rating.

  5. Question 5

    Q5. In a molecule of 1,3-butadiene (CH2=CH-CH=CH2), what is the total number of sigma bonds and pi bonds present respectively?

    • A) 9 sigma, 2 pi
    • B) 7 sigma, 2 pi
    • C) 11 sigma, 2 pi
    • D) 9 sigma, 1 pi

    Answer: 9 sigma, 2 pi

    Explanation: Includes six C-H and three C-C sigma bonds. 7 sigma is wrong because it forgets C-H bonds.

  6. Question 6

    Q6. A specific organic compound has an empirical formula of CH2O and a molar mass of 60 g/mol. What is the total number of oxygen atoms in one molecule?

    • A) 1
    • B) 2
    • C) 3
    • D) 4

    Answer: 2

    Explanation: Molecular formula is C2H4O2 based on molar mass 60. 1 is wrong as it is only the empirical ratio.

  7. Question 7

    Q7. During the combustion analysis of 0.20 g of an organic compound, 0.18 g of water was collected. What is the percentage of hydrogen in this compound?

    • A) 11.1%
    • B) 9.0%
    • C) 20.1%
    • D) 5.5%

    Answer: 11.1%

    Explanation: Hydrogen mass is calculated using 2/18 of water mass. 9% is wrong because it neglects the H2 molar ratio.

  8. Question 8

    Q8. If an organic molecule undergoes sp2 hybridization, what is the theoretical percentage of s-character present in each hybrid orbital?

    • A) 25.0%
    • B) 50.0%
    • C) 33.3%
    • D) 66.7%

    Answer: 33.3%

    Explanation: One s and two p orbitals create three hybrids. 25% is wrong because that applies to sp3 hybridization only.

  9. Question 9

    Q9. A sample of urea [CO(NH2)2] is analyzed for its nitrogen content. What is the mass percentage of nitrogen in pure urea?

    • A) 23.3%
    • B) 28.0%
    • C) 60.0%
    • D) 46.6%

    Answer: 46.6%

    Explanation: Urea contains two nitrogen atoms (28g) in 60g total. 23.3% is wrong because it counts only one nitrogen atom.

  10. Question 10

    Q10. In the molecule of propyne (CH3-C≡CH), how many sigma bonds are formed by the overlap of sp-sp3 hybridized carbon orbitals?

    • A) 1
    • B) 2
    • C) 3
    • D) 4

    Answer: 1

    Explanation: This bond exists between the sp3 methyl carbon and the sp triply-bonded carbon. 2 is wrong, counting pi bonds.

  11. Question 11

    Q11. A hydrocarbon with the formula C6H6 is analyzed. If it is an open-chain dipropyne, how many pi bonds must it contain to satisfy the valency?

    • A) 3
    • B) 4
    • C) 5
    • D) 2

    Answer: 4

    Explanation: C6H6 requires four pi bonds to satisfy carbon valency in open chains. 3 is wrong, being specific to benzene's ring.

  12. Question 12

    Q12. A 1.47 g sample of an organic halide yields 2.87 g of AgCl in Lassaigne's test. What is the percentage of chlorine in the compound?

    • A) 35.5%
    • B) 24.1%
    • C) 48.3%
    • D) 71.0%

    Answer: 48.3%

    Explanation: Calculated from chlorine mass in AgCl relative to sample. 35.5% is wrong, confusing atomic mass with actual percentage.

  13. Question 13

    Q13. In the reforming process, n-octane is converted to 2,2,4-trimethylpentane. What is the change in the number of primary carbons between these two isomers?

    • A) 1
    • B) 3
    • C) 5
    • D) 2

    Answer: 3

    Explanation: Iso-octane has five primary carbons while n-octane has two. 1 is wrong, misidentifying the number of terminal methyl groups.

  14. Question 14

    Q14. A student observes a molecule of naphthalene. Based on its structural formula, how many pi electrons are delocalized across the ring system?

    • A) 5
    • B) 6
    • C) 12
    • D) 10

    Answer: 10

    Explanation: Each of the five double bonds contributes two pi electrons. 5 is wrong because it counts bonds instead of electrons.

  15. Question 15

    Q15. A compound contains 40% Carbon, 6.7% Hydrogen, and 53.3% Oxygen. If its molecular mass is 180, what is the number of carbon atoms per molecule?

    • A) 1
    • B) 3
    • C) 6
    • D) 12

    Answer: 6

    Explanation: The empirical formula CH2O (30g) fits six times into 180g. 3 is wrong, representing the empirical mass ratio instead.

  16. Question 16

    Q16. If the bond angle in a specific hydrocarbon is measured at 109.5 degrees, what is the percentage of p-character in the hybrid orbitals of the central carbon?

    • A) 75%
    • B) 25%
    • C) 50%
    • D) 100%

    Answer: 75%

    Explanation: sp3 hybrids consist of 25% s and 75% p character. 25% is wrong because it refers to the s-character instead.

  17. Question 17

    Q17. How many structural isomers are possible for a compound with the molecular formula C3H8O?

    • A) 1
    • B) 2
    • C) 3
    • D) 4

    Answer: 3

    Explanation: Includes two alcohols and one ether. 2 is wrong because students often forget the functional isomerism of ethers.

  18. Question 18

    Q18. A cracking reaction converts C10H22 into C6H14 and two moles of an alkene. What is the molecular formula of this alkene?

    • A) C2H4
    • B) C3H6
    • C) C4H8
    • D) CH4

    Answer: C2H4

    Explanation: Balancing the equation C10H22 -> C6H14 + 2C2H4. C4H8 is wrong as it ignores the two-mole coefficient provided.

  19. Question 19

    Q19. In a sample of ethyne (C2H2), what is the total number of shared electron pairs (bonds) specifically between the two carbon atoms?

    • A) 2
    • B) 3
    • C) 5
    • D) 6

    Answer: 3

    Explanation: The triple bond in ethyne consists of three shared electron pairs. 2 is wrong, confusing it with the double bond.

  20. Question 20

    Q20. A heterocyclic compound, Pyridine (C5H5N), is analyzed. What is the mass percentage of the heteroatom in this molecule? (C=12, H=1, N=14)

    • A) 14.0%
    • B) 21.5%
    • C) 12.6%
    • D) 17.7%

    Answer: 17.7%

    Explanation: Nitrogen (14g) divided by the total molar mass (79g). 14% is wrong, using an incorrect total molecular weight.

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