To determine which reaction occurs most rapidly at room temperature, let's analyze the nature of the reactants and products in each reaction:
### A. Silver nitrate reacting with sodium chromate:
[tex]\[ 2 \text{AgNO}_{3(\text{aq})} + \text{Na}_2\text{CrO}_{4(\text{aq})} \rightarrow \text{Ag}_2\text{CrO}_{4(\text{s})} + 2 \text{NaNO}_{3(\text{aq})} \][/tex]
- This reaction involves two ionic compounds in aqueous solution.
- Ionic reactions in aqueous solutions tend to occur very rapidly because the ions are free to move and interact in the solution.
### B. Calcium oxide reacting with carbon:
[tex]\[ \text{CaO}_{(\text{s})} + 3 \text{C}_{(\text{s})} \rightarrow \text{CaC}_{2(\text{s})} + \text{CO}_{(\text{g})} \][/tex]
- This reaction involves solid reactants and a gaseous product.
- Solid-state reactions are generally slower as the reactants must come into physical contact, which is less frequent.
### C. Tin(IV) oxide reacting with carbon monoxide:
[tex]\[ \text{SnO}_{2(\text{s})} + 2 \text{CO}_{(\text{g})} \rightarrow \text{Sn}_{(\text{s})} + 2 \text{CO}_{2(\text{g})} \][/tex]
- This reaction involves both a solid and a gas.
- Reactions involving solids and gases tend to have slower rates compared to reactions in aqueous solutions.
### D. Iron reacting with oxygen:
[tex]\[ 2 \text{Fe}_{(\text{s})} + \text{O}_{2(\text{g})} \rightarrow 2 \text{FeO}_{(\text{s})} \][/tex]
- This reaction involves a solid reactant (iron) and a gaseous reactant (oxygen).
- Similar to the previous solid-gas reaction, the rate of reaction is generally slower at room temperature.
### Conclusion:
Among the given reactions, the reaction of silver nitrate with sodium chromate (reaction A) involves ionic compounds in aqueous solution, which tends to proceed more rapidly due to the high mobility and interaction rate of ions in solution. Therefore, reaction A occurs most rapidly at room temperature.
The correct answer is:
[tex]\[ \boxed{A} \][/tex]
