Resposta :
[tex]\boxed{\begin{array}{l}\sf Fe+S\longrightarrow FeS\\\sf56~g~de~Fe\longrightarrow32~g~de~S\\\sf 28~g~de~Fe\longrightarrow k\\\sf 56k=28\cdot32\\\sf k=\dfrac{\diagdown\!\!\!\!\!\!28^1\cdot32}{\diagdown\!\!\!\!\!\!56_2}\\\sf k=\dfrac{32}{2}\\\sf k=16~g~de~S\\\sf para~formar~28~de~Fe~basta~16~g~de~S.\\\sf no~exerc\acute icio~foi~dado~64~g~de~S\\\sf o~que~nos~leva~a~concluir~que~S~\acute e~reagente~em~excesso.\\\sf56 g~de~Fe\longrightarrow88~g~de~FeS\\\sf28 g~de~Fe\longrightarrow x\end{array}}[/tex]
[tex]\boxed{\begin{array}{l}\sf56x=28\cdot88\\\sf x=\dfrac{\diagdown\!\!\!\!\!\!28\cdot88}{\diagdown\!\!\!\!\!\!56_2}\\\sf x=\dfrac{88}{2}\\\sf x=44~g~de~FeS\\\huge\boxed{\boxed{\boxed{\boxed{\sf\maltese~alternativa~a}}}}\end{array}}[/tex]