Free Isotopes questions for IGCSE Chemistry (0620), part of Atoms, elements & compounds. Each question has the answer and the marking points an examiner would look for.
Generate a full Isotopes worksheet →All Atoms, elements & compounds questionsTwo isotopes of the same element are compared.
1 They have the same chemical properties.
2 They have the same electronic configuration.
3 They have the same number of neutrons.
Which statements are correct?
Answer: B
A sample of boron contains 20% of 10B and 80% of 11B.
What is the relative atomic mass of boron in this sample?
Answer: C
Which statement describes relative atomic mass?
Answer: C
This question is about the element gallium.
Gallium has two isotopes, gallium-69 and gallium-71. State what is meant by isotopes.
State the number of protons, neutrons and electrons in one atom of gallium-71.
Explain why the two isotopes have the same chemical properties.
A sample of gallium contains 61% gallium-69 and 39% gallium-71. Calculate the relative atomic mass of gallium. Give your answer to one decimal place.
Define relative atomic mass.
Give the electronic configuration of an atom of gallium and use it to predict the group of the element.
Explain, in terms of the particles in the nucleus, why the relative atomic mass of gallium is not a whole number.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | atoms of the same element with the same number of protons, different numbers of neutrons atoms of the same element / same proton number B1 different numbers of neutrons / nucleon numbers B1 | 2 |
| (b) | 31, 40, 31 protons 31 and electrons 31 B1 neutrons 40 B1 | 2 |
| (c) | same number of electrons in the outer shell same electronic configuration / same number of outer electrons B1 | 1 |
| (d) | 69.8 (69 × 61 + 71 × 39)/100 M1 69.8 A1 | 2 |
| (e) | average mass of the isotopes compared to 1/12 of a carbon-12 atom average mass of the isotopes of an element (weighted by abundance) B1 compared with 1/12 of the mass of an atom of carbon-12 B1 | 2 |
| (f) | 2,8,18,3; Group III 2,8,18,3 B1 Group III B1 | 2 |
| (g) | it is a weighted average of isotopes with different masses it is a weighted average of the masses of isotopes that have different numbers of neutrons B1 | 1 |
Carbon has isotopes carbon-12, carbon-13 and carbon-14.
Complete the number of protons, neutrons and electrons in a carbon-14 atom.
Explain why carbon-14 has the same chemical reactions as carbon-12.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 6, 8, 6 protons 6 B1 neutrons 8 B1 electrons 6 B1 | 3 |
| (b) | same electron configuration same number of electrons/same electronic configuration B1 | 1 |
Chlorine has two isotopes, chlorine-35 and chlorine-37.
Define isotopes.
Explain why the isotopes have the same chemical properties.
Naturally occurring chlorine is 75% chlorine-35 and 25% chlorine-37. Calculate the relative atomic mass.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | same protons, different neutrons atoms of the same element / same number of protons B1 with different numbers of neutrons B1 | 2 |
| (b) | same electronic configuration they have the same number of electrons in the outer shell / same electronic configuration B1 | 1 |
| (c) | 35.5 (75 × 35 + 25 × 37) ÷ 100 C1 35.5 A1 | 2 |
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Meet Riyaz →Original Cambridge-style practice questions written for mentorriyaz.in. These are not Cambridge past paper questions, and this site is not affiliated with or endorsed by Cambridge University Press & Assessment. Updated 2026-11-04. Paper generator · mentorriyaz.in