* Identify the charges: Iron (Fe) typically has a +2 charge in ionic compounds, while sulfur (S) usually has a -2 charge.
* Balance the charges: In FeS₂, there's one iron atom (Fe²⁺) and two sulfur atoms (S⁻). To achieve neutrality, the sulfur atoms must have a combined charge of -4 (to balance the +2 from iron).
* Calculate the valency of sulfur: Since there are two sulfur atoms, each sulfur atom must have a valency of -2.
Therefore, the valency of sulfur in FeS₂ is -2.
