AS Level Chemistry chapter 11: Group 17 MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

88 exam-style questions on Group 17, 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.

88 questions · 4 topics · 10 per test

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What chapter 11 covers

Ten Group 17 questions with answers

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

1. What are the products when chlorine reacts with hot concentrated aqueous sodium hydroxide?

  1. A
    NaCl, NaClO and H2O
  2. B
    NaCl and H2O only
  3. C
    NaClO3, H2 and O2
  4. D
    NaCl, NaClO3 and H2O
Show answer

Answer: D. In hot alkali the chlorate(I) that forms disproportionates further, so the products are sodium chloride, sodium chlorate(V), NaClO3, and water.

2. Excess chlorine is bubbled into 25.0 cm3 of 0.0800 mol dm−3 aqueous potassium iodide. What is the maximum mass of iodine, I2, formed? (Ar: I = 126.9)

  1. A
    0.0635 g
  2. B
    0.127 g
  3. C
    0.254 g
  4. D
    0.508 g
Show answer

Answer: C. n(I−) = 0.0250 × 0.0800 = 2.00 × 10−3 mol; two I− give one I2, so 1.00 × 10−3 mol × 253.8 = 0.254 g. 0.508 g assumes one I2 per I−; 0.127 g uses Ar(I) instead of Mr(I2).

3. Samples of Cl2, Br2 and I2 vapour are heated to the same high temperature. Which is the most dissociated into atoms?

  1. A
    Cl2
  2. B
    Br2
  3. C
    I2
  4. D
    all three equally
Show answer

Answer: C. The I–I bond is the longest and weakest of the three, so least energy is needed to break it and iodine dissociates most at a given temperature.

4. When a solution of sodium chlorate(I) is heated it reacts: 3NaClO → 2NaCl + NaClO3. Which statement is correct?

  1. A
    chlorine is only reduced, from +1 to −1
  2. B
    no oxidation numbers change, so this is not a redox reaction
  3. C
    sodium is oxidised and chlorine is reduced
  4. D
    chlorine is oxidised from +1 to +5 and reduced from +1 to −1, so this is disproportionation
Show answer

Answer: D. Two Cl atoms go from +1 to −1 (gaining 4 electrons) and one goes from +1 to +5 (losing 4 electrons). The same element is both oxidised and reduced, which is why hot alkali gives chlorate(V).

5. Which list shows the halide ions in order of increasing strength as reducing agents?

  1. A
    I−, Br−, Cl−
  2. B
    Br−, Cl−, I−
  3. C
    Cl−, I−, Br−
  4. D
    Cl−, Br−, I−
Show answer

Answer: D. Down the group the halide ion is larger and its outer electrons are more shielded, so it loses electrons more easily. Iodide is the strongest reducing agent and chloride the weakest.

6. The enthalpy change of vaporisation of bromine is about 30 kJ mol−1, but the Br–Br bond energy is 193 kJ mol−1. Why is the enthalpy change of vaporisation so much smaller?

  1. A
    Boiling breaks only half of the Br–Br bonds.
  2. B
    Boiling overcomes only the id-id forces between Br2 molecules; no covalent bonds are broken.
  3. C
    Bromine is a liquid, so its Br–Br bonds are already partly broken.
  4. D
    The Br–Br bond becomes stronger in the gas phase.
Show answer

Answer: B. Bromine vapour is still made of Br2 molecules, so vaporisation only separates the molecules by overcoming weak id-id forces. Breaking the covalent Br–Br bond needs far more energy.

7. Household bleach is made by passing chlorine into cold dilute aqueous sodium hydroxide. Which compound in the bleach is the active oxidising agent?

  1. A
    NaCl
  2. B
    NaOH
  3. C
    NaClO3
  4. D
    NaClO
Show answer

Answer: D. Cold alkali gives NaCl and NaClO; the chlorate(I) ion, with Cl at +1, is the oxidising agent. NaClO3 forms only with hot alkali.

8. Which equation shows the reaction of chlorine with water that produces the species used to kill bacteria in water treatment?

  1. A
    Cl2 + H2O ⇌ 2HOCl
  2. B
    Cl2 + H2O ⇌ HCl + HOCl
  3. C
    Cl2 + H2O ⇌ Cl2O + H2
  4. D
    Cl2 + 2H2O ⇌ 2HCl + H2O2
Show answer

Answer: B. Chlorine disproportionates in water to HCl and HOCl, chloric(I) acid. HOCl and the ClO− ion it forms are the active species; the equation giving 2HOCl is not balanced for hydrogen.

9. Which ionic equation represents the reaction of chlorine with aqueous potassium iodide?

  1. A
    Cl2 + 2I− → 2Cl− + I2
  2. B
    Cl2 + I− → 2Cl− + I
  3. C
    Cl− + I2 → Cl2 + I−
  4. D
    2Cl + I2 → 2Cl− + 2I+
Show answer

Answer: A. Chlorine is the stronger oxidising agent and takes electrons from iodide ions. Atoms and charge balance: two Cl, two I and a total charge of −2 on each side.

10. Aqueous silver nitrate is added to aqueous potassium iodide, followed by concentrated aqueous ammonia. What is seen?

  1. A
    a white precipitate that dissolves in the ammonia
  2. B
    a cream precipitate that dissolves in the ammonia
  3. C
    a yellow precipitate that does not dissolve in the ammonia
  4. D
    no precipitate at any stage
Show answer

Answer: C. Silver iodide is a yellow precipitate that is insoluble even in concentrated ammonia. A white precipitate soluble in dilute ammonia would mean chloride.

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Ways to practise this chapter

Group 17: questions students ask

How many Group 17 MCQs are there?

88, each with the answer and a short explanation, across 4 topics: Physical properties of the Group 17 elements, The chemical properties of the halogen elements and the hydrogen halides, Some reactions of the halide ions, The reactions of chlorine. Every chapter test draws ten of them, so you can take it many times.

Is the AS Level Chemistry chapter 11 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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