Answer: C. There are 3 magnesium for every 2 bromine
Explanation: The formula Mg3Br2 represents the compound formed from the reaction between Magnesium metal and bromine. The compound is usually called magnesium bromide formed from ionic or eoectrovalent bonding of magnesium and bromine. The compound's could be interpreted to mean for there to attain stability, there are 3 magnesium ions for every 2 bromine.
(Mg^2+) + (Br^-1)