which of the following reactions is an example of autoreduction?

1.FeS+3/2(O₂)----->FeO+SO₂

2.FeO+SiO₂------>FeSiO₃.

3.Cu₂O+1/2(Cu₂S)------>3Cu+1/2(SO₂).

4.Cu₂S+3/2(O₂)-------->Cu2O+SO₂.

reduction reaction is a type of reaction in which the oxidation number decreases
in case of 3^rdreaction the oxidation number changes from +1 to 0 so the elment reduces its oxidation number
Cu2O+1/2(Cu2S)------>3Cu+1/2(SO2
in case ofFeS+3/2(O2)----->FeO+SO2 andCu2S+3/2(O2)-------->Cu2O+SO2.the oxidation number does not change it remins same