Exam-style question
Try this first
Which statement best explains why two atoms of the same element can have different masses?.
- A.They have different numbers of protons.
- B.They have different numbers of electrons.
- C.They have different numbers of neutrons.
- D.They have different numbers of photons.
Model answer
What a good answer should say
- They have different numbers of neutrons.
Explanation
Why this works
Isotopes of an element have the same proton number (defining the element) but differ in neutron number, giving different atomic masses. This matches the objective of explaining isotopes using neutron number.
Common mistake
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