Lesson 3.1.1.2

3.1.1.2 Mass number and isotopes Quiz: AQA Chemistry, Unit 1

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.1.1.2, Mass number and isotopes: 20 multiple choice questions for the AQA Chemistry (7405), Unit 1: Physical chemistry, written with Revision Ninja.

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The 20 questions

  1. What fundamental particles are added together to calculate mass number?

    • Protons and neutrons
    • Quarks and leptons
    • Neutrons and electrons
    • Protons and electrons

  2. What does the atomic number (Z) of an atom represent?

    • Protons plus neutrons
    • Number of protons
    • Number of electrons
    • Number of neutrons

  3. Atoms of the same element with different neutron numbers are called what?

    • Isomers
    • Ions
    • Allotropes
    • Isotopes

  4. What do all ions gain during acceleration in a TOF mass spectrometer?

    • Same charge
    • Same momentum
    • Same velocity
    • Same kinetic energy

  5. Which ions reach the detector first in a TOF mass spectrometer?

    • Slowest ions
    • Heavier ions
    • Lighter ions
    • Uncharged particles

  6. What information does a mass spectrometer give about isotopes?

    • Mass and abundance
    • Proton count only
    • Radius and charge
    • Charge and speed

  7. Which molecular quantity can be determined using a mass spectrometer?

    • Bond dissociation energy
    • Relative atomic radius
    • Empirical formula mass
    • Relative molecular mass

  8. Chlorine has isotopes 35Cl and 37Cl in relative abundance 75% and 25%. What is the relative atomic mass of chlorine?

    • 36.0
    • 35.0
    • 37.0
    • 35.5

  9. Boron has isotopes 10B (19.9%) and 11B (80.1%). What is the relative atomic mass of boron to two decimal places?

    • 10.00
    • 10.50
    • 10.80
    • 11.00

  10. An ion contains 26 protons, 30 neutrons and 23 electrons. What are its mass number and charge?

    • 56 and -3
    • 56 and +1
    • 30 and +3
    • 56 and +3

  11. A neutral atom has a mass number of 81 and 46 neutrons. How many electrons does it have?

    • 35
    • 81
    • 46
    • 127

  12. Two isotopes of the same element differ in their number of which particle?

    • Positrons
    • Electrons
    • Protons
    • Neutrons

  13. A mass spectrum shows peaks at m/z 35 and 37 in a 3:1 ratio. What do these peaks represent?

    • Two elements
    • Two allotropes
    • Isobars
    • Two isotopes

  14. An element has a relative atomic mass of 69.7 and is made of two isotopes, 69 and 71. What is the approximate percentage abundance of the 71 isotope?

    • 65%
    • 85%
    • 35%
    • 15%

  15. An atom has a mass number of 24 and 12 neutrons. Which proton number and element does it correspond to?

    • Z = 24, chromium
    • Z = 12, sodium
    • Z = 12, magnesium
    • Z = 12, carbon

  16. Element M has isotopes 85M (72%) and 87M (28%). What is its relative atomic mass?

    • 86.00
    • 85.00
    • 85.56
    • 87.00

  17. Why does the relative atomic mass of an element always lie between its smallest and largest isotopic masses?

    • Weighted mean mass
    • Most abundant mass
    • Sum of masses
    • Simple mean mass

  18. In a TOF mass spectrometer, which ion reaches the detector first?

    • Lowest m/z ratio
    • Highest mass ion
    • Highest m/z ratio
    • Uncharged molecule

  19. A sample has the isotopic composition 24Mg 79%, 25Mg 10% and 26Mg 11%. What is the relative atomic mass to two decimal places?

    • 25.00
    • 24.50
    • 24.32
    • 24.00

  20. Why do carbon-12 and carbon-14 have identical chemical properties?

    • Different proton numbers
    • Same neutron count
    • Same electron configuration
    • Same mass number

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