What this tests
Syllabus point 3.1 — Formulae, in Stoichiometry. Difficulty easy (estimated from the question's demands, not a Cambridge rating).
Also set in
The same question, as Cambridge printed it in other papers.
Cambridge IGCSE Chemistry 0620 · 3.1 Formulae
June 2014 · Paper 11 · Question 9
One real Cambridge question from Stoichiometry, with the official answer. Cambridge has printed this question 2 times.