Blank #1: Polyatomic
Blank #2: 2 (see explanation)
Blank #3: 1 (see explanation)
Both the ammonium ion [tex]\text{NH}_4^{+}[/tex] and the sulfate ion [tex]\text{SO}_4^{2-}[/tex] contain more than one atom in each ion. The two species are thus polyatomic. The chloride ion [tex]\text{Cl}^{-}[/tex], for example, is monoatomic.
Superscripts above formulae of the ions indicate their charge. Each ammonium ion carries a positive one (+1) charge. Each sulfate ion carries a charge of negative two (-2).
Ammonium sulfate is an ionic compound. A sample of this compound contain myriads of ammonium ions and sulfate ions. The ions are packed in three-dimensional lattices. Thus unlike water, ammonium sulfate does not exist as molecules in nature.
Assuming that the second and third blanks refers to a formula unit, rather than a molecule, of ammonium sulfate. The empirical formula of ammonium sulfate gives the minimum whole-number ratio between the two ions in a sample.
Charges shall balance between the two ions. Ammonium ions are of charge +1. Sulfate ions are of charge -2. The sample shall thus contain two ammonium ions for every one sulfate ion.
The empirical formula of ammonium sulfate is therefore [tex](\text{NH}_4)_2\text{SO}_4[/tex].
There are thus two ammonium ions [tex]\text{NH}_4^{+}[/tex] and one sulfate ion [tex]\text{SO}_4^{2-}[/tex] in each formula unit of ammonium sulfate.
The compound ammonium sulfate consists of two ions, NH4+ and SO42–, both of which are polyatomic ions. A molecule of the compound consists of two NH4+ ion(s) and one SO42– ion(s).
