Nerve agent that is the most persistent is very oily and will stay active in an area for several days?

The nerve agent you are referring to is likely VX (venomous agent X). VX is known for its high persistence in the environment due to its oily texture, which allows it to remain active on surfaces for an extended period, often several days. This characteristic makes VX particularly dangerous in terms of contamination and exposure, as it can pose a threat long after its initial deployment. Proper handling and decontamination procedures are crucial when dealing with such agents.