Final answer:
In the reaction 2Cr(s) + 3O₂(g) → 2CrO₃(s), two chromium atoms combine with six oxygen atoms, making option d (six) the correct answer.
Step-by-step explanation:
In the chemical reaction 2Cr(s) + 3O₂(g) → 2CrO₃(s), two chromium atoms combine with six oxygen atoms. The correct answer to the question is option d. six. This stoichiometry is evident from the balanced chemical reaction, which requires two moles of chromium atoms to react fully with three moles of diatomic oxygen (O₂) molecules. Each O₂ molecule consists of two oxygen atoms, thus three O₂ molecules contain a total of 3 × 2, which equals six oxygen atoms.