Chemistry: The Central Science (13th Edition)

$CaBr_{2}$
The overall charge of the compound must be neutral. The problem gives the charge of Calcium (Ca), +2, and the charge of Bromine (Br), -1. To cancel out the +2 of the Calcium ion, there must be two Bromine ions, for Bromine ions only have a charge of -1 while Calcium ions have a charge of +2. Thus, the compound is $CaBr_{2}$.