What is most likely to make a rock crack or crumble?

Rocks are most likely to crack or crumble due to weathering processes, which include physical, chemical, and biological factors. Physical weathering, such as freeze-thaw cycles, causes water to seep into cracks, freeze, and expand, leading to fragmentation. Chemical weathering can alter the mineral composition of rocks, weakening their structure. Additionally, biological weathering from plant roots or microorganisms can exert pressure or produce acids that further break down rock material.