Some plant fertilizer compounds are $\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}, \mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}$ $\mathrm{K}_{2} \mathrm{O}, \mathrm{P}_{2} \mathrm{O}_{5},$ and $\mathrm{KCl}$ . Which of these compounds contain both ionic and covalent bonds?