#### Answer

a. BaS
b. Li^2O
c. Ca^3N^2
d. CuI^2

#### Work Step by Step

a. Barium's charge is plus 1, and sulfates charge is minus 1, so it balances. Therefore you can simply write BaS.
b. Lithium has a charge of plus 1, while oxygen has a charge of minus 2. To balance oxygen's, you must have two lithiums. Therefore you write Li^2O.
c. For this problem you use this criss cross method, since the charges are not divisible. Therefore, you simply move the plus 2 charge of calcium over to nitrate, and vice versa.
d. Copper has a charge of plus 2, while iodine's has a charge of minus 1. Therefore, to balance out coppers positive charge, you need two iodines. The formula is CuI^2