Fumigants are defined as pesticides that:

Fumigants are a specific category of pesticides that are applied as gases. This gaseous form allows them to penetrate soil or other materials effectively, making them useful for controlling pests in various environments, such as stored products, warehouses, and soil treatments. The volatile nature of fumigants enables them to disperse and diffuse through the area being treated, which enhances their efficacy in pest control.

While some other options may pertain to different types of pesticides or formulations, they do not accurately describe fumigants. For example, fumigants are not limited to being liquid or solid, nor do they inherently require high pressure for application. Their primary characteristic is that they are gaseous during application, which distinguishes them from other pesticide formulations. This understanding is crucial for proper application and ensuring safety during use.