IGCSE Physics 5.1 The Nuclear Atom MCQs – 30 Practice Questions with Answers (Cambridge 0625)

Free practice MCQs for Cambridge IGCSE Physics 0625, Section 5.1 The Nuclear Atom, covering the Rutherford alpha-scattering experiment, the particles inside the atom, and proton number, nucleon number and isotopes. Every question is an original practice question with a worked answer – tap Show Answer to check yourself as you revise.

Formula recap: Number of neutrons = A − Z | In a neutral atom, number of electrons = number of protons = Z | Isotopes have the same Z but a different A. Revise every key fact with the full IGCSE Physics Formula Sheet.

Rutherford Scattering & the Nuclear Model

Q1. In the alpha-particle scattering experiment, most alpha particles passed straight through the gold foil with little or no deflection. What does this observation show?

  • (A) The atom is a solid sphere of positive charge
  • (B) The nucleus takes up most of the volume of the atom
  • (C) Most of the atom is empty space
  • (D) Alpha particles carry no charge
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Answer: C – If the atom were solid or filled with charge, most alpha particles would have been deflected. Passing straight through shows that most of the atom is empty space, with the mass and charge concentrated in a tiny nucleus.

Q2. A few alpha particles in the experiment were deflected through very large angles, some by more than 90 degrees. This is evidence that the nucleus is:

  • (A) Small, dense and positively charged
  • (B) Large, light and negatively charged
  • (C) Spread evenly throughout the atom
  • (D) Made entirely of neutrons
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Answer: A – Only a small, dense, positively charged centre can repel an alpha particle strongly enough to turn it through a large angle. A spread-out charge would produce only tiny deflections.

Q3. An alpha particle passing close to a gold nucleus is pushed away from it. This happens because:

  • (A) The nucleus has no electric charge
  • (B) The alpha particle is negatively charged
  • (C) The alpha particle is attracted towards the electrons
  • (D) The alpha particle and the nucleus are both positively charged, and like charges repel
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Answer: D – An alpha particle carries a positive charge of +2 and the nucleus is also positive. Like charges repel, so the alpha particle is deflected away from the nucleus, most strongly when it passes closest.

Q4. Only about 1 in 8000 alpha particles bounced straight back from the gold foil. This rare event shows that:

  • (A) Electrons have a very large mass
  • (B) The nucleus is very small compared with the whole atom but contains most of its mass
  • (C) The alpha particles were travelling too slowly
  • (D) Gold atoms contain no empty space
Show Answer

Answer: B – A head-on collision with the nucleus is needed for a bounce-back, and this almost never happens because the nucleus is tiny. When it does happen, the alpha particle rebounds because the nucleus is much more massive than the alpha particle.

Q5. In the plum-pudding model of the atom:

  • (A) Electrons orbit a tiny central nucleus
  • (B) Protons and neutrons are packed together in the centre
  • (C) Negative electrons are embedded in a uniform ball of positive charge
  • (D) The atom is completely empty
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Answer: C – The plum-pudding model pictured the atom as a sphere of positive charge (the “pudding”) with negative electrons (the “plums”) embedded in it. Rutherford’s results replaced it with the nuclear model.

Q6. Which result of the scattering experiment could the plum-pudding model NOT explain?

  • (A) Alpha particles being deflected through very large angles
  • (B) Some alpha particles passing through the foil
  • (C) The foil being made of atoms
  • (D) Alpha particles travelling in straight lines through air
Show Answer

Answer: A – In the plum-pudding model the positive charge is spread thinly over the whole atom, so the repulsive force on an alpha particle is far too weak to cause large-angle deflections. The nuclear model, with charge concentrated in a tiny nucleus, explains them.

Q7. The gold foil used in the experiment was made extremely thin so that:

  • (A) The experiment would be cheaper to perform
  • (B) All of the alpha particles would be stopped by the foil
  • (C) The foil would not melt under the beam
  • (D) Each alpha particle passed through only a few atoms, so any deflection was caused by a single atom
Show Answer

Answer: D – With a very thin foil, each alpha particle meets only a few atoms, so a large deflection can be credited to one close encounter with a single nucleus rather than many small deflections adding up.

Q8. The alpha particles in Rutherford’s experiment were detected using:

  • (A) A thermometer placed behind the foil
  • (B) A fluorescent screen that gave a tiny flash of light where each particle landed
  • (C) A photographic film sensitive only to X-rays
  • (D) An ammeter measuring an electric current
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Answer: B – Each alpha particle striking the fluorescent (zinc sulfide) screen produced a small flash of light, which the experimenters observed through a microscope and counted at different angles.

Q9. Alpha particles that travelled far from any nucleus were hardly deflected at all. This is because:

  • (A) They were moving too fast to be affected
  • (B) The electrons pushed them back onto a straight path
  • (C) The repulsive force from a nucleus is very weak at large distances, and most of the atom is empty space
  • (D) Gold nuclei have no charge at large distances
Show Answer

Answer: C – The electric repulsion falls rapidly with distance, so only alpha particles passing very close to a nucleus feel a strong force. Most pass through empty space far from any nucleus and continue almost straight.

Q10. Which statement correctly describes the nuclear model of the atom?

  • (A) The positive charge is spread evenly through the whole atom
  • (B) Electrons are packed inside the nucleus
  • (C) The nucleus occupies most of the volume of the atom
  • (D) At the centre of the atom is a tiny nucleus containing protons and neutrons, with electrons around it
Show Answer

Answer: D – The nuclear model places a tiny, dense, positive nucleus (protons and neutrons) at the centre, with electrons in the space around it. The nucleus holds almost all the mass but almost none of the volume.

Protons, Neutrons & Electrons

Q11. What are the relative charge and relative mass of a neutron?

  • (A) Charge 0, relative mass 1
  • (B) Charge +1, relative mass 1
  • (C) Charge −1, relative mass 1/1840
  • (D) Charge 0, relative mass 1/1840
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Answer: A – A neutron has no electric charge (0) and a relative mass of 1, about the same as a proton. The particle with charge −1 and relative mass 1/1840 is the electron.

Q12. Where in the atom are the protons and neutrons found?

  • (A) In the shells around the centre
  • (B) Spread evenly throughout the atom
  • (C) Orbiting the centre of the atom
  • (D) Packed together in the nucleus
Show Answer

Answer: D – Protons and neutrons are the particles of the nucleus (together they are called nucleons). Electrons are the particles found in the space or shells around the nucleus.

Q13. In a neutral atom, the number of electrons is equal to the number of:

  • (A) Neutrons
  • (B) Protons
  • (C) Nucleons
  • (D) Atoms
Show Answer

Answer: B – Each proton has charge +1 and each electron has charge −1. For the atom to be neutral overall, the numbers must be equal: number of electrons = number of protons = Z.

Q14. The relative mass of an electron is approximately:

  • (A) 1
  • (B) 1840
  • (C) 1/1840
  • (D) Exactly 0
Show Answer

Answer: C – An electron has a relative mass of about 1/1840, so roughly 1840 electrons would be needed to equal the mass of one proton. This is why the electron’s mass is often treated as negligible.

Q15. Almost all of the mass of an atom is concentrated in its nucleus because:

  • (A) Each proton and neutron has about 1840 times the mass of an electron
  • (B) The nucleus takes up most of the atom’s volume
  • (C) Electrons move too quickly to have any mass
  • (D) The nucleus also contains all of the electrons
Show Answer

Answer: A – Protons and neutrons (relative mass 1 each) sit in the nucleus, while the electrons outside have a relative mass of only 1/1840 each. So the nucleus, although tiny, contains almost all the mass.

Q16. An atom has a diameter of about 10−10 m and its nucleus has a diameter of about 10−14 m. The diameter of the nucleus is smaller than the diameter of the atom by a factor of about:

  • (A) 100
  • (B) 10 000
  • (C) 4
  • (D) 1 000 000
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Answer: B – Factor = 10−10 / 10−14 = 104 = 10 000. The nucleus is about ten thousand times smaller in diameter than the atom, which is why the atom is mostly empty space.

Q17. Which particle has a relative charge of −1?

  • (A) Proton
  • (B) Neutron
  • (C) Nucleus
  • (D) Electron
Show Answer

Answer: D – The electron has relative charge −1. The proton has relative charge +1 and the neutron has charge 0; the nucleus as a whole is positive because of its protons.

Q18. A nucleus contains 8 protons and 8 neutrons. What is the total charge of this nucleus, in units of the elementary charge?

  • (A) 0
  • (B) +16
  • (C) +8
  • (D) −8
Show Answer

Answer: C – Only the protons contribute charge: 8 protons × (+1) = +8. The 8 neutrons are uncharged, so they add mass but no charge.

Q19. If an atom were enlarged to the size of a football stadium, its nucleus would be roughly the size of:

  • (A) A football on the centre spot
  • (B) A small pea at the centre of the pitch
  • (C) The centre circle of the pitch
  • (D) One of the stands
Show Answer

Answer: B – The nucleus is about 10 000 times smaller in diameter than the atom, so on the stadium scale it shrinks to about the size of a pea at the centre – yet it still holds almost all of the atom’s mass.

Q20. Which statement about the particles in an atom is correct?

  • (A) Electrons are found in shells around the nucleus
  • (B) Neutrons move in shells around the nucleus
  • (C) Protons are found outside the nucleus
  • (D) Electrons are packed inside the nucleus
Show Answer

Answer: A – Electrons occupy the space around the nucleus, arranged in shells. Protons and neutrons are both inside the nucleus; no electrons are found there.


Proton Number, Nucleon Number & Isotopes

Q21. The proton number (atomic number) Z of an atom is the number of:

  • (A) Neutrons in the nucleus
  • (B) Nucleons in the nucleus
  • (C) Protons plus neutrons in the nucleus
  • (D) Protons in the nucleus
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Answer: D – Z counts the protons only. The nucleon number A counts protons + neutrons, and Z is what decides which element the atom is.

Q22. A sodium nucleus is written as 2311Na. How many neutrons does it contain?

  • (A) 11
  • (B) 12
  • (C) 23
  • (D) 34
Show Answer

Answer: B – Number of neutrons = A − Z = 23 − 11 = 12. The lower number (11) is the proton number and the upper number (23) is the nucleon number.

Q23. A neutral atom of oxygen is written as 168O. How many electrons does it contain?

  • (A) 8
  • (B) 16
  • (C) 24
  • (D) 0
Show Answer

Answer: A – Z = 8, so the atom has 8 protons. In a neutral atom the number of electrons equals the number of protons, so it has 8 electrons (and 16 − 8 = 8 neutrons).

Q24. Isotopes of an element are atoms that have:

  • (A) The same nucleon number but different proton numbers
  • (B) The same number of neutrons but different numbers of protons
  • (C) The same proton number but different nucleon numbers
  • (D) Different numbers of protons and different numbers of electrons
Show Answer

Answer: C – Isotopes share the same proton number Z (so they are the same element) but contain different numbers of neutrons, giving different nucleon numbers A and different masses.

Q25. Which pair of nuclei are isotopes of the same element?

  • (A) 146C and 147N
  • (B) 126C and 168O
  • (C) 4018Ar and 4019K
  • (D) 126C and 146C
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Answer: D – Isotopes must have the same Z but different A. Both carbon nuclei have Z = 6, while their nucleon numbers are 12 and 14. In options A and C the A values match but Z differs, so those are different elements.

Q26. A uranium nucleus is written as 23892U. How many neutrons does it contain?

  • (A) 92
  • (B) 146
  • (C) 238
  • (D) 330
Show Answer

Answer: B – Number of neutrons = A − Z = 238 − 92 = 146. The nucleus also contains 92 protons, and 92 + 146 = 238 nucleons in total.

Q27. An atom loses two electrons and becomes an ion. What happens to its proton number and its nucleon number?

  • (A) Both stay the same; only the overall charge of the atom changes
  • (B) The proton number decreases by 2
  • (C) The nucleon number decreases by 2
  • (D) Both the proton number and the nucleon number decrease by 2
Show Answer

Answer: A – Ionisation only removes electrons from the shells; the nucleus is untouched, so Z and A are unchanged. Losing two negative electrons simply leaves the ion with an overall charge of +2.

Q28. Isotopes of the same element have identical chemical properties. This is because they have the same number of:

  • (A) Neutrons
  • (B) Nucleons
  • (C) Electrons in a neutral atom
  • (D) Atoms
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Answer: C – Chemical behaviour is fixed by the electron arrangement. Isotopes have the same proton number, so their neutral atoms have the same number of electrons and react in the same way, even though their masses differ.

Q29. A nucleus contains 17 protons and 20 neutrons. What are its proton number Z and nucleon number A?

  • (A) Z = 20, A = 37
  • (B) Z = 17, A = 20
  • (C) Z = 37, A = 17
  • (D) Z = 17, A = 37
Show Answer

Answer: D – Z is simply the proton count: Z = 17. A counts all the nucleons: A = 17 + 20 = 37. This nucleus would be written as 3717Cl.

Q30. A neutral atom of helium is written as 42He. Which row gives the correct numbers of protons, neutrons and electrons?

  • (A) Protons 2, neutrons 4, electrons 2
  • (B) Protons 2, neutrons 2, electrons 2
  • (C) Protons 4, neutrons 2, electrons 4
  • (D) Protons 2, neutrons 2, electrons 4
Show Answer

Answer: B – Z = 2 gives 2 protons. Neutrons = A − Z = 4 − 2 = 2. The atom is neutral, so electrons = protons = 2.

Keep practising: Work through more topics on the Physics MCQs hub page and keep the key facts handy with the IGCSE Physics Formula Sheet.

All questions on this page are original practice questions written for QuaidianPoint – they are not Cambridge past-paper questions.