* Limestone is primarily composed of calcium carbonate (CaCO3). Acids react with calcium carbonate to form calcium salts, carbon dioxide, and water. This reaction is a common way that limestone is weathered and eroded.

Let's look at why the other options are less likely:

* Gneiss, granite, and schist are all igneous or metamorphic rocks. While they may contain some minerals that react with acids, they are generally more resistant to chemical weathering than limestone.

In summary: Limestone is the most susceptible to forming new compounds when exposed to acidic air pollution due to its chemical composition.