What elements are represented by the symbols in each of the following substances?
a. fireworks, $\mathrm{KNO}_{3}$
b. dental cement, $\mathrm{Zn}_{3}\left(\mathrm{PO}_{4}\right)_{2}$
c. antacid, $\mathrm{Mg}(\mathrm{OH})_{2}$
d. manufacture of aluminum, $\mathrm{AlF}_{3}$