Answer
a. $Cl^-$
b. $HS{O_3}^-$
c. $CH{O_2}^-$
d. $F^-$
Work Step by Step
1. Remove one hydrogen from their formulas:
a. $Cl$
b. $HSO_3$
c. $CHO_2$
d. $F$
2. Decrease their charges by one:
a. $Cl^-$
b. $HS{O_3}^-$
c. $CH{O_2}^-$
d. $F^-$