Question detail
An element has an atomic number of 20 and a mass number of 40. How many neutrons does this element have (A-level cue 4de082ab focus)
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Atomic structure
Question
- A. 20
- B. 40 (A-level cue 4de082ab distractor 1)
- C. 60 (A-level cue 4de082ab distractor 2)
- D. 80 (A-level cue 4de082ab distractor 3)
Answer
20
Explanation
The correct option is 20. 20 is correct because it supports the objective: Report isotope and mass-spectrometry calculations to an appropriate number of significant figures.. The reasoning stays within Mass number, isotopes and mass spectrometry and avoids drifting into a similar A-Level Chemistry idea. This version is uniquely anchored to Mass number, isotopes and mass spectrometry. Retrieval anchor: A-level cue 4de082ab.
Common mistake
Significant Figures Mistake
Students often report the relative atomic mass of an isotope without considering significant figures, leading to inaccurate results.
To fix this, identify the number of significant figures required based on the data provided. For example, if the isotopic abundance data is given to three significant figures, ensure your final answer is also reported to three significant figures. Use the formula for relative atomic mass: relative atomic mass = (Σ(isotopic mass × abundance)) / Σ(abundance). Substitute the values, perform the calculation, and round the final answer appropriately.
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