The formula unit of compounds formed depends on the valency of the combining ions.
The formula unit is the smallest unit of an ionic substance that gives us a picture of the ratio in which ions are combined in the ionic compound.
Usually, the formula unit is written based on the valency of the ions.
For the ions listed;
Li+ and 02- forms Li2O
Mg2+ and S2- forms MgS
A13+ and CI- forms AlCl3
Na+ and N3- forms Na3N
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