Question 1Warm-upFoundation
Uranium-238 () decays by alpha emission into thorium. What are the mass number and atomic number of the thorium?
Alpha: −4 from the top, −2 from the bottom.
Worked solution
- and
Answer:
GCSE & IGCSE physics practice
Nuclear equations questions and answers
Nuclear equations show radioactive decay. In alpha decay the nucleus loses an alpha particle (): the mass number falls by 4 and the atomic number by 2. In beta decay a neutron becomes a proton and an electron () is emitted: the mass number stays the same and the atomic number rises by 1. Gamma emission changes neither.
8 questions · Foundation tier · Every answer is checked as you type it, with a full worked solution. Updated .
Where nuclear equations comes up
| GCSE (AQA) | Physics and Combined Science, Foundation and Higher: use nuclear equations for alpha, beta and gamma decay. |
|---|---|
| Cambridge IGCSE (0625) | Supplement (Extended): use decay equations in nuclide notation to show the emission of α-particles, β-particles and γ-radiation. |
The method
- Alpha: mass number − 4, atomic number − 2.
- Beta: mass number unchanged, atomic number + 1.
- Gamma: no change to either.
- Check: the mass numbers (top) and atomic numbers (bottom) balance on both sides.
Nuclear equations questions
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Warm-up
Question 2Warm-upFoundation
Carbon-14 () decays by beta emission into nitrogen. What are the mass number and atomic number of the nitrogen?
Beta: the mass number stays the same; the atomic number goes up by 1.
Worked solution
- Mass number ; atomic number
Answer:
Exam-style
Question 3Exam-styleFoundation
Radium-226 () decays by alpha emission into radon. Give the radon's mass number and atomic number.
Alpha decay.
Worked solution
- and
Answer:
Question 4Exam-styleFoundation
A nucleus decays. Its mass number stays the same and its atomic number goes up by 1. What was emitted?
Which decay turns a neutron into a proton?
Worked solution
- In beta decay a neutron becomes a proton (atomic number +1) and an electron is emitted (no change in mass number).
Answer: A beta particle
Question 5Exam-styleFoundation
What happens to the mass number and atomic number when a nucleus emits gamma radiation?
Gamma has no mass and no charge.
Worked solution
- A gamma ray carries away energy only, so the nucleus keeps the same mass number and atomic number.
Answer: Neither changes: gamma rays are electromagnetic waves
Question 6Exam-styleFoundation
Polonium-210 () decays by alpha emission into lead. Give the lead's mass number and atomic number.
Alpha decay.
Worked solution
- and
Answer:
Challenge
Question 7ChallengeFoundation
Thorium-234 () decays by beta emission. Give the mass number and atomic number of the new nucleus.
Beta decay.
Worked solution
- Mass number ; atomic number
Answer: (protactinium)
Question 8ChallengeFoundation
Uranium-238 () decays by one alpha emission followed by two beta emissions. Give the mass number and atomic number of the final nucleus.
Do one step at a time.
Worked solution
- After alpha:
- After two betas: atomic number , mass number still
- Atomic number 92 is uranium, so the result is uranium-234.
Answer: : uranium again, a different isotope
Common mistakes
- Subtracting 2 from the mass number in alpha decay.
- Making the atomic number go down in beta decay.
- Forgetting that a new atomic number means a new element.
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Sources
The questions are our own. The “where it comes up” notes are from each board's published specification, checked on 27 October 2026:
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