Case study·Standard multi-step (3/5)·No calculator
Difficulty guide
The label describes the problem, not your ability.
1/5 - Foundational
Warm-up setup; checks one basic idea.
2/5 - Routine exam skill
Normal syllabus skill; usually one main rule or interpretation.
3/5 - Standard multi-step
Exam-style problem with multiple steps or a common trap.
4/5 - Hard exam skill
High-end exam problem; combines methods carefully.
5/5 - Challenge
Stretch problem beyond normal exam pressure.
Question
A hospital uses a radioactive isotope of iodine in a controlled diagnostic test. Another atom of iodine used in ordinary chemistry has the same atomic number but a different mass number.
Total: 3 marks
(a) Why are the two iodine atoms isotopes? (1 mark)
(b) Which number must be the same in both atoms? (1 mark)
(c) Which subatomic particle count is different? (1 mark)
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