What is the maximum amount of propane that can be transported in an enclosed vehicle at one time?

The maximum amount of propane that can be transported in an enclosed vehicle at one time is indeed 90 pounds. This limit is established by regulations which focus on safety during transport, particularly concerning flammable gases like propane. When propane is transported, it poses risks such as explosion or fire, especially if there is a leak.

By limiting the amount to 90 pounds, regulations aim to minimize the potential hazards associated with transporting larger quantities of highly flammable materials. This consideration is critical to ensure both the safety of the transporter and the public.

Each of the other options exceeds this safety limit, which explains why they are not correct. Therefore, 90 pounds is designed as a safe threshold for transport in an enclosed vehicle, reflecting a balance between operational needs and safety regulations.