Final answer:
The last stage of physical weathering in rocks is frost action (b) from the provided options, as it is part of the mechanical weathering processes, whereas chemical weathering is a separate kind of weathering.
Step-by-step explanation:
The last stage of physical weathering in rocks is not listed in the options provided, as chemical weathering is a separate process. Physical weathering, also known as mechanical weathering, includes processes like frost action, abrasion, thermal expansion, and biological activity. Of the provided options, frost action (b) can be considered the last stage since abrasion and biological activity also contribute to mechanical weathering without signaling an endpoint to the process.
Option (d) chemical weathering is incorrect as it pertains to a different type of weathering that involves a chemical change, such as the oxidation of minerals or dissolution by acidic solutions. Examples from different exercises clarified that physical changes, like ice melting, and physical abrasion from wind or water fall under physical weathering, whereas chemical weathering includes chemical changes like the alteration of feldspar to clay in the formation of clastic sedimentary rocks.