Name a chemical which becomes explosive when it becomes dry:

Picric acid is correctly identified as a chemical that becomes explosive when it dries out. When picric acid, also known as 2,4,6-trinitrophenol, is in its hydrated form, it is relatively stable. However, as it dries, it tends to form a more hazardous condition because the crystal structure becomes more sensitive to shock, heat, and friction. The dried form of picric acid can detonate under certain conditions, making it a significant safety concern in laboratories and storage environments.

Other options mentioned, such as benzoic acid, nitric acid, and ethyl alcohol, do not exhibit the same explosive characteristics upon drying. Benzoic acid is generally regarded as a low-hazard substance, nitric acid is a strong oxidizer but does not explode when dry, and ethyl alcohol is flammable but not explosive. This distinction helps clarify why picric acid is notable for its explosive potential in a dry state.