To combine ions to form ionic compounds, we need the combine in such a way that it gets neutral charge.
We can combine each anion with each cation to get the 4 compounds we need.
To combine SO₄²⁻ with Pb⁴⁺ we first find the Least Common Multiple of their charges, 2 and 4.
They have the factor 2 in common, so the LCM is 4. This is the final charge of each that will cancel out.
To get 4+, we only need 1 Pb⁴⁺.
To get 4-, we need 2 SO₄²⁻.
So, the formula is:
Pb(SO₄)₂
To combine SO₄²⁻ with NH₄⁺ is easier because one of them has single charge. In this case, we can simply pick one of the multiple charge ion and the same amount that will cancel its charge of the single charged one.
So, we picke 1 SO₄²⁻, ending with 2-.
And we picke 2 NH₄⁺, ending with 2+.
The formula:
(NH₄)₂SO₄
To combine C₂H₃O₂⁻ with Pb⁴⁺ we do the same, because the anion is single charged.
Pick 1 Pb⁴⁺, ending with 4+.
Pick 4 C₂H₃O₂⁻, ending with 4-.
The formula:
Pb(C₂H₃O₂)₄
To combine C₂H₃O₂⁻ with NH₄⁺, both have same charge, so we just need one of each and their charges will cancel out.
The formula:
NH₄C₂H₃O₂
So, the formulas are:
Pb(SO₄)₂
(NH₄)₂SO₄
Pb(C₂H₃O₂)₄
NH₄C₂H₃O₂