Which of the following reactions occurs most rapidly at room temperature?

a. 2AgNO3 (aq) + Na2CrO4 (aq) → Ag2CrO4 (s) + 2NaNO3 (aq)

b. CaO (s) + 3C (s) → CaC2 (s) + CO (g)

c. SnO2 (s) + 2CO (g) → Sn (s) + 2CO2 (g)

d. 2Fe (s) + O2 (g) → 2FeO (s)

I think the correct answer from the choices listed above is option A. The reaction that occurs most rapidly at room temperature would be 2AgNO3 (aq) + Na2CrO4 (aq) → Ag2CrO4 (s) + 2NaNO3 (aq). T his is an ionic reaction involving simple exchange of ions in a solution after which the insoluble silver chromate precipitates down.