Edexcel IGCSE Chemistry 1.17 Relative atomic mass
Practise calculating Ar from isotope abundance data, including percentage tables, rounding and simple isotope probabilities.
- Syllabus
- First assessment 2019
- Course
- Chemistry 4CH1
Practise calculating Ar from isotope abundance data, including percentage tables, rounding and simple isotope probabilities.
This question is about Group 2 elements and their compounds.
A sample of magnesium contains three isotopes.

Calculate the relative atomic mass (Ar) of magnesium.
Give your answer to one decimal place.
- (76.5 x 24) + (10.5 x 25) + (13.0 x 26)
- divide by 100
- 24.4
Marking guidance:
- 24.365 is an acceptable unrounded intermediate answer.
- Correct answer without working scores 3.
- 24 with no working scores 0.