Which of the following metals reacts with the moist carbon dioxide in the air and slowly loses its shiny brown surface and gains a green coat?

Copper

The correct answer is option 4. Copper.

The metal that reacts with moist carbon dioxide in the air, slowly losing its shiny brown surface and gaining a green coat, is Copper.

When copper reacts with moist carbon dioxide in the air, it forms a greenish layer of copper carbonate \((CuCO_3)\), which is known as copper patina or verdigris. This greenish coat gradually develops over time and gives copper objects their characteristic greenish appearance, such as the Statue of Liberty.