Using the periodic table, choose the more reactive nonmetal.
Br or As

Reactivity of non-metals depend on their ability to gain electrons. So, smaller is the size of a non-metal more readily it will attract electrons because then nucleus will be more closer to valence shell. ... Hence, Br is the non-metal which will be more reactive than At.

br is more reactive than as

there is none because earth is stationary and flat.