The reaction representing the Mond process for metal refining is ______

The Mond process is used for refining nickel. It involves the following steps:

Impure nickel reacts with carbon monoxide at 330-350 K to form volatile nickel tetracarbonyl:

Nickel tetracarbonyl is decomposed at higher temperature (450-470 K) to give pure nickel:

Let us check the other options:

Option B: $$2\text{K[Au(CN)}_2] + \text{Zn} \rightarrow \text{K}_2[\text{Zn(CN)}_4] + 2\text{Au}$$ — This is the MacArthur-Forrest (cyanide) process for gold.

Option C: $$\text{Zr} + 2\text{I}_2 \rightarrow \text{ZrI}_4$$ — This is the Van Arkel process for zirconium/titanium.

Option D: $$\text{ZnO} + \text{C} \rightarrow \text{Zn} + \text{CO}$$ — This is carbon reduction, not a refining process.

The answer is Option A: $$\text{Ni} + 4\text{CO} \xrightarrow{\Delta} \text{Ni(CO)}_4$$.