Answer
(a) Mg(NO$_2$)$_2$
(b) Li$_3$PO$_4$
(c) Ba(CN)$_2$
(d) (NH$_4$)$_2$SO$_4$
Work Step by Step
(a) Mg(NO$_2$)$_2$
Magnesium (Mg) is an alkaline earth metal and has a valence of 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 nitrite (NO$_2$$^-$). We will need one magnesium ion for every two nitrite ions to balance the charges in this compound.
(b) Li$_3$PO$_4$
Lithium (Li) is an alkali metal and has a valence of 1+. We refer to the table of polyatomic anions (Table 2.2) on page 65 of the book to find the formula and charge for phosphate (PO$_4$$^{3-}$). We will need three lithium ions for every one phosphate ion to balance the charges in this compound.
(c) Ba(CN)$_2$
Barium (Ba) is an alkaline earth metal and has a valence of 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 cyanide (CN$^-$). We will need one barium ion for every two cyanide ions to balance the charges in this compound.
(d) (NH$_4$)$_2$SO$_4$
The ammonium ion (NH$_4$$^+$) has a valence of 1+. We refer to the table of polyatomic anions (Table 2.2) on page 65 of the book to find the formula and charge for sulfate (SO$_4$$^{2-}$). We will need two ammonium ions for every one sulfate ion to balance the charges in this compound.
