Final answer:
The overall reaction for the formation of phosgene (COCl2) from CO and Cl2 is CO(g) + Cl2(g) → COCl2(g). This corresponds to option (c) in the multiple-choice question provided by the student.
Step-by-step explanation:
The overall reaction for the formation of phosgene (COCl2) from carbon monoxide (CO) and chlorine gas (Cl2) is given by the reaction: CO(g) + Cl2(g) → COCl2(g).
This can be determined by adding the elementary steps of the mechanism provided and canceling out intermediate species that appear on both the reactant and product side of the combined equations:
Cl2(g) = 2Cl(g) (fast)
CO(g) + Cl(g) → COCl(g) (slow)
COCl(g) + Cl(g) → COCl2(g) (fast)
Adding these steps and canceling out intermediate Cl radicals which appear on both sides of the reaction, we get:
CO(g) + Cl2(g) → COCl2(g)
Note that the other species, COCl(g), is an intermediate and does not appear in the final reaction equation. Thus, the correct answer to the student's original multiple-choice question is (c).