Answer : The number of moles of sulfur needed to oxidize will be, 3 moles
Solution : Given,
Moles of zinc = 3 moles
The balanced reaction will be,

By the stoichiometry, 1 mole of
ion react with the 1 mole of
to give 1 mole of zinc sulfide.
From the balanced reaction, we conclude that
As, 1 mole of zinc react with 1 mole of sulfur
So, 3 moles if zinc react with 3 moles of sulfur
Hence, the number of moles of sulfur needed to oxidize will be, 3 moles