Which of the following substances is not soluble in water and can create explosive conditions?

Flammable oils, while they are not soluble in water, can indeed create explosive conditions under certain circumstances. When flammable oils enter water bodies, they can float on the surface, forming an oil slick. If a sufficient quantity of these oils accumulates, they pose a risk of ignition, especially in the presence of heat or sparks, leading to potentially explosive situations.

Oils and greases, while also not soluble in water and capable of causing environmental issues, do not typically create explosive conditions in the manner that flammable oils can when ignited. Similarly, organic toxicants and toxic gases don't primarily present explosive hazards directly, although they can be harmful or hazardous in other ways.

Thus, recognizing the nature of flammable oils in terms of their physical properties and behavior in relation to water helps clarify why they can create hazardous explosive conditions in specific environments.