Answer
(a) Ba$^{2+}$
(b) ClO$_4$$^-$
(c) Co$^{2+}$
(d) SO$_4$$^{2-}$
Work Step by Step
(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-}$).
