Which of the following weeds produces a milky, acrid sap that can irritate the skin?

Spurges are known for producing a milky, acrid sap that can be irritating to the skin. This characteristic sap contains compounds that can cause skin irritation or allergic reactions in some individuals upon contact. The presence of this sap is a notable feature of spurges, distinguishing them from other weed types. When handling spurges, it is advisable to wear gloves and take precautions to avoid skin contact.

The other options do not possess the same type of sap that has skin-irritating properties. Thistles, for example, may have sharp spines, while dandelions and chickweeds do not produce a sap with similar irritative qualities. Understanding these characteristics can help identify spurges more easily and highlight the need for appropriate handling procedures for the safety of those dealing with these plants.