Karst topography is formed by the reaction of carbonic acid with calcium carbonate (CaCO3).

Here's why:

* Carbonic acid (H2CO3) is formed when carbon dioxide (CO2) dissolves in water. This is a natural process, as rainwater absorbs CO2 from the atmosphere.

* Calcium carbonate (CaCO3) is the primary component of limestone, a sedimentary rock.

* The chemical reaction: When carbonic acid comes into contact with calcium carbonate, it dissolves the calcium carbonate, creating caves, sinkholes, and other characteristic features of karst topography. The reaction can be summarized as:

CaCO3 + H2CO3 → Ca(HCO3)2

This reaction produces calcium bicarbonate (Ca(HCO3)2), which is soluble in water.

So, the formation of karst topography is a result of the dissolution of limestone by carbonic acid.