Is this MgCl2, KCl, or K2SO4?

Method 1 :

In the diagram, each cation carries 1 positive charge, while each anion carries 2 negative charges.

For MgCl₂, each Mg²⁺ cation carries 2 positive charges, while each Cl⁻ anion carries 1 negative charge.
For KCl, each K⁺ cation carries 1 positive charge, while each Cl⁻ anion carries 1 negative charge.
For K₂SO₄, each K⁺ cation carries 1 positive charge, while each SO₄²⁻ anion carries 2 negative charges.

Only the charges carried by the ions of K₂SO₄ match the charges carries by the ions of the compound in the diagram.
The answer: K₂SO₄


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Method 2 :

In the diagram, (No. of cations) : (No. of anions) = 8 : 4 = 2 : 1

For MgCl₂, (No. of Mg²⁺ cations) : (No. of Cl⁻ anions) = 1 : 2
For KCl, (No. of K⁺ cations) : (No. of Cl⁻ anions) = 1 : 1
For K₂SO₄, (No. of K⁺ cations) : (No. of SO₄²⁻ anions) = 2 : 1

Only the number ratio of the opposite ions of K₂SO₄ matches the number ratio of opposite ions of the compound in the diagram.
The answer: K₂SO₄

There are two 2- ions for each 1+ ion, so the formula must look like MX2, so it must be MgCl2.