## Chemistry: Principles and Practice (3rd Edition)

(a) Ba$^{2+}$ (b) ClO$_4$$^- (c) Co^{2+} (d) SO_4$$^{2-}$
(a) Ba$^{2+}$ From the periodic table, we see that barium (Ba) is an alkaline earth metal belonging to group 2 and, thus, has a valence of 2+. (b) ClO$_4$$^- We refer to the table of polyatomic anions (Table 2.2) on page 65 of the book to find the formula and charge for perchlorate (ClO_4$$^-$). (c) Co$^{2+}$ We are looking at cobalt (II), which means that the valence for this particular atom of cobalt has a valence of 2+. (d) SO$_4$$^{2-} We refer to the table of polyatomic anions (Table 2.2) on page 65 of the book to find the formula and charge for sulfate (SO_4$$^{2-}$).