\(a,3Fe+2O_2\rightarrow\left(t^o\right)Fe_3O_4\\ n_{O_2}=\dfrac{6}{24}=0,25\left(mol\right)\\ n_{Fe_3O_4}=\dfrac{23,2}{232}=0,1\left(mol\right)\\ b,\dfrac{0,1}{1}< \dfrac{0,25}{2}\Rightarrow O_2dư\\ n_{O_2\left(con.du\right)}=0.25-0,1.2=0,05\left(mol\right)\\ V_{O_2\left(con.du\right)}=0,05.24=1,2\left(l\right)\)