Calculate, showing your working, the relative atomic mass, ${A_{\text{r}}}$, of magnesium, giving your answer to two decimal places.

$({A_{\text{r}}} = ){\text{ }}0.7899 \times 24 + 0.1000 \times 25 + 0.1101 \times 26$;

24.32;

Award [2] for correct final answer.

Award [1 max] for 24.31 with correct working.

Award [0] for 24.31 (Data Booklet value) if working is incorrect or no working is shown.

Final answer must be to 2 decimal places to score [2].

This question generally scored well. The processes involved in a mass spectrometer were well understood; except for the importance of forming a cation. The calculation of ${A_{\text{r}}}$ and the requirement to give an answer to two decimal places was performed very well.