When dealing with compounds and their names, it helps to know the prefixes of some of the common compounds. For instance,
Mono- = 1
Di- = 2
Tri- = 3
Tetra- = 4
Penta- = 5
Hexa- = 6
And the list goes on.
However we are dealing with Arsenic Hexabromide:
That means we have 1 Arsenic with 6 Bromides:
[tex] AsBr_{6} [/tex]
