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 is the mass number (A) of an atom?

    • The number of protons plus neutrons
    • The number of neutrons only
    • The number of electrons plus neutrons
    • The number of protons only

  2. What is the atomic (proton) number, Z, of an atom?

    • The total number of nucleons in the atom
    • The number of protons in the nucleus
    • The number of electrons in the outer shell
    • The number of neutrons in the nucleus

  3. Which statement defines isotopes?

    • Ions of the same element with the same charge
    • Atoms of the same element with different numbers of electrons
    • Atoms of different elements with the same mass number
    • Atoms of the same element with different numbers of neutrons

  4. In a simple time of flight mass spectrometer, what is the purpose of the acceleration stage?

    • To detect the ions at the end of the tube
    • To separate ions by their colour
    • To ionise the sample molecules
    • To give all ions the same kinetic energy

  5. What property of an ion determines how quickly it travels through a time of flight mass spectrometer?

    • Its colour and the wavelength of light it absorbs in the tube
    • Its number of neutrons, with heavier isotopes arriving first
    • Its mass to charge ratio, with lighter ions arriving first
    • Its size, with the largest ions arriving first at the detector

  6. According to the specification, what does a mass spectrometer give accurate information about?

    • Relative isotopic mass and the relative abundance of isotopes
    • Rates of reaction and the activation energy at different temperatures
    • Enthalpy changes for reactions carried out at constant pressure
    • Bond angles and molecular shapes within simple covalent molecules

  7. Which quantity can a mass spectrometer be used to determine for a molecule?

    • Its enthalpy of combustion
    • Its boiling point directly
    • Its bond angle
    • Its 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. An atom of element X has mass number 81 and 46 neutrons. What is its proton number, and how many electrons does the neutral atom have?

    • Proton number 35, and 35 electrons
    • Proton number 81, and 81 electrons
    • Proton number 46, and 46 electrons
    • Proton number 35, and 46 electrons

  12. Two isotopes of an element have mass numbers 63 and 65. Which statement about them is correct?

    • They have the same number of neutrons and different numbers of electrons
    • They have the same mass number but different numbers of electrons
    • They have different numbers of protons and the same number of neutrons
    • They have the same number of protons and different numbers of neutrons

  13. A mass spectrum of a sample shows peaks for ions of mass 35 and 37 in the ratio 3:1. What does this show?

    • The sample contains two different compounds of equal mass
    • The sample contains an ion with a charge of 2+
    • The sample is pure, with only one isotope present
    • The sample contains two isotopes of one element in roughly a 3:1 ratio

  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. A gallium sample has an Ar of 69.7 and is made of isotopes 69Ga and 71Ga. Why must the Ar lie between 69 and 71?

    • Ar is a weighted mean of the isotopic masses, so it must lie between the masses of the isotopes present
    • Ar is always the simple arithmetic mean of the two mass numbers, which means abundances do not matter
    • Ar is the sum of the isotopic mass numbers, divided by the number of electrons present in the atom
    • Ar is always the mass of the heaviest isotope present, because heavier isotopes dominate the average value

  18. In a time of flight mass spectrometer, all ions are accelerated through the same potential difference. Which ion reaches the detector first?

    • The lightest ion with the largest charge
    • The heaviest ion with the largest charge
    • The heaviest ion with the smallest charge
    • The lightest ion with the smallest charge

  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. Which statement correctly explains why 12C and 14C have the same chemical properties?

    • They are the same nuclide and therefore have identical mass numbers and nuclear properties
    • They have the same mass number, which means they contain identical numbers of protons
    • They have the same number of electrons and the same electron configuration
    • They have the same number of neutrons, so their nuclei behave identically in reactions

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