Answer
a. $N{H_4}^+$
b. $HClO_4$
c. $H_2SO_4$
d. $HCO{_3}^-$
Work Step by Step
1. Add one hydrogen to their formulas:
a. $NH_4$
b. $HCl{O_4}^-$
c. $HS{O_4}^-$
d. $HC{O_3}^{2-}$
2. Increase their charges by one:
a. $N{H_4}^+$
b. $HClO_4$
c. $H_2SO_4$
d. $HCO{_3}^-$