Blank #1: Polyatomic
Blank #2: 2 (see explanation)
Blank #3: 1 (see explanation)
<h3>Explanation</h3>
Both the ammonium ion 
and the sulfate ion 
contain more than one atom in each ion. The two species are thus <em>polyatomic</em>. The chloride ion 
, for example, is <em>monoatomic</em>.
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 
.
There are thus two ammonium ions and one sulfate ion in each formula unit of ammonium sulfate.
1)An element forms a positive ion when it loses an electron called Cation, whereas it forms a negative ion when it gains an electron called Anion.
2) Cations have smaller atomic radii than that of an Anions.
3) Metals have the tendency to form Cations by losing an electron, while non metals have tendency to form Anions by gaining an electron.
4) etc
The balanced equation for the neutralisation reaction is as follows
2LiOH + H₂SO₄ ---> Li₂SO₄ + 2H₂O
stoichiometry of LiOH to H₂SO₄ is 2:1
both LiOH and H₂SO₄ are strong bases and strong acids respectively, therefore they completely ionise into their respective ions
1 mol of H₂SO₄ is neutralised by 2 mol of H₂SO₄
therefore 2.0 mol of H₂SO₄ is neutralised by - 2 x 2.0 = 4.0 mol of LiOH
4.0 mol of LiOH is required to neutralise 2.0 mol of H₂SO₄
This is a double replacement or double displacement reaction
