Answer
Please see the work below.
Work Step by Step
We know that
a. The given formula $Mg(IO_4)_2$ is incorrect and the correct formula is $Mg(IO_3)_2.$
b. The given formula $H_3PO_3$ is incorrect and the correct formula is $H_3PO_4.$
c. The given formula $BaS$ is correct.
d. The given formula $NH_3HCO_3$ is incorrect and the correct formula is $NH_4HCO_3.$