Here's why:

* Location on the periodic table: Bromine is located in Group 17 (also known as the halogens) of the periodic table. All elements in this group are nonmetals.

* Physical properties: Bromine exists as a reddish-brown liquid at room temperature, which is a characteristic of nonmetals. It is also a poor conductor of heat and electricity, unlike metals.

* Chemical properties: Bromine is highly reactive and readily forms compounds with other elements, another characteristic of nonmetals.