Explain why it is dangerous to burn a carbon-based fuel, such as propane or methane, in a closed room or building.

Setting a fire too or burning substances such as propane or methane in a closed room/building can very easily cause an open flame or fire to the area because they are flammable substances 

☆ionisation energy increases across a period from na -> ar☆ionisation energy decreases down a group from li -> fr☆ionic radius decreases across a period from na -> cl☆ionic radius increases down a groupfrom f -> ii hope it clarifies your doubts

There are no metaphors.