The answer is B, bench.
A chair is a piece of furniture with a seat and back, typically for one person to sit on. A bench is a long seat for several people to sit on, typically with no back. A table is a piece of furniture with a flat top supported by legs, used for eating, working, or playing games. A stool is a seat without a back, typically with three legs.
The word “bench” is different from the rest because it is the only word that does not refer to a piece of furniture that is used for sitting. A chair, table, and stool are all pieces of furniture that are used for sitting, but a bench is not. A bench is typically used for sitting in a group, such as on a park bench or a school bench.