Work Step by Step
This is an ionic compound, so the cation is what is listed first (Cobalt). The Roman numerals tell us that the cation has a charge of 2+. The anion is what is listed second (Hydrogen Carbonate). This anion has a formula of $HCO_3$, and a charge of -1. To have a neutral compound, there needs to be twice as many Hydrogen Carbonate molecules as Cobalt, hence $Co(HCO_3)_2$.