IB Diploma Chemistry chapter 3: Structure 3: Classification of matter MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

22 exam-style questions on Structure 3: Classification of matter, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

22 questions · 2 topics · 10 per test

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What chapter 3 covers

Ten Structure 3: Classification of matter questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. Why do boiling points increase from methane to butane?

  1. A
    longer molecules have more electrons and more surface contact, so London forces are stronger
  2. B
    hydrogen bonding increases with chain length
  3. C
    the C–H bonds become stronger
  4. D
    the molecules become more polar
Show answer

Answer: A. Alkanes are non-polar; only London forces act between them, and these grow with the number of electrons and area of contact. Boiling does not break C–H bonds.

2. Which statement about a homologous series is correct?

  1. A
    all members have the same boiling point
  2. B
    all members are structural isomers of each other
  3. C
    members share a general formula and successive members differ by CH2
  4. D
    members have different functional groups
Show answer

Answer: C. A homologous series has the same functional group and general formula, similar chemistry, and a gradual trend in physical properties. Isomers have the same molecular formula, which homologues do not.

3. Why does atomic radius decrease across period 3 from sodium to chlorine?

  1. A
    the number of occupied energy levels decreases
  2. B
    electrons repel each other more strongly
  3. C
    the atoms contain more neutrons, which attract the electrons
  4. D
    nuclear charge increases while electrons are added to the same energy level with similar shielding
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Answer: D. Each step adds a proton, but the new electron goes into the same main level, so shielding barely changes and the outer electrons are pulled closer.

4. What is the IUPAC name of CH3CH(CH3)CH2CH3?

  1. A
    3-methylbutane
  2. B
    2-methylbutane
  3. C
    2-ethylpropane
  4. D
    pentane
Show answer

Answer: B. The longest chain has four carbons (butane), with a methyl group numbered from the nearer end: 2-methylbutane. 3-methylbutane numbers from the wrong end.

5. Which compound is a tertiary halogenoalkane?

  1. A
    CH3CH2CH2CH2Br
  2. B
    CH3CHBrCH2CH3
  3. C
    (CH3)2CHCH2Br
  4. D
    (CH3)3CBr
Show answer

Answer: D. In a tertiary halogenoalkane the carbon bonded to the halogen is attached to three other carbons, as in 2-bromo-2-methylpropane. A branched chain alone does not make it tertiary.

6. Which general trend in first ionization energy is correct?

  1. A
    it increases down group 1
  2. B
    it decreases across a period
  3. C
    it increases across a period and decreases down a group
  4. D
    it is the same for every element in a group
Show answer

Answer: C. Across a period nuclear charge rises with similar shielding, so electrons are held more tightly; down a group the outer electron is further away and more shielded.

7. Which oxide reacts with water to form an acidic solution?

  1. A
    SO3
  2. B
    MgO
  3. C
    Na2O
  4. D
    CaO
Show answer

Answer: A. Non-metal oxides are acidic: SO3 + H2O → H2SO4. The metal oxides form alkaline hydroxide solutions.

8. How many structural isomers with the molecular formula C4H10O are alcohols?

  1. A
    2
  2. B
    3
  3. C
    4
  4. D
    7
Show answer

Answer: C. butan-1-ol, butan-2-ol, 2-methylpropan-1-ol and 2-methylpropan-2-ol: four alcohols. Seven counts the three ethers as well, which are not alcohols.

9. Which equation represents the first electron affinity of chlorine?

  1. A
    ½Cl2(g) + e− → Cl−(g)
  2. B
    Cl(g) + e− → Cl−(g)
  3. C
    Cl(g) → Cl+(g) + e−
  4. D
    Cl−(g) → Cl(g) + e−
Show answer

Answer: B. Electron affinity is the energy change when one mole of gaseous atoms each gains one electron. Starting from Cl2 would include bond breaking; losing an electron is ionization.

10. What is the oxidation state of sulfur in the thiosulfate ion, S2O32−?

  1. A
    +2
  2. B
    +4
  3. C
    +6
  4. D
    −2
Show answer

Answer: A. 2x + 3(−2) = −2, so 2x = +4 and x = +2 (an average over the two S atoms). Forgetting the ion charge gives +3, and ignoring that there are two S atoms gives +4.

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Structure 3: Classification of matter: questions students ask

How many Structure 3: Classification of matter MCQs are there?

22, each with the answer and a short explanation, across 2 topics: S3.1 The periodic table: classification of elements, S3.2 Functional groups: classification of organic compounds. Every chapter test draws ten of them, so you can take it many times.

Is the IB Diploma Chemistry chapter 3 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

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