a. The lowest priority ligand `(H)` is in the plane not on the dotted line) so it make two interchanges such that `H` is projected away from the observer. (Priority order: `-NH_(2) gt -CH_(2)CH_(3) gt -CH_(3) gt -H`)
b. The lowest priority ligand `(H)` is on the dotted line. `R` and `S` can be assigned directly from the priority rule. `(-OH gt- CHO gt-CH_(2)OH gt -H)`
c. Lowest priority ligand `(-CH_(3))` is in the plance (i.e., not on th dotted line). So make one interchange so that `(-CH_(3))` is projechted away from the observer. (Priority order `-Cl gt -SH gt -CH_(2)CH_(3) gt -CH_(3))`
