\(a,PTHH:3Fe+2O_2\rightarrow^{t^o}Fe_3O_4\\ b,n_{Fe_3O_4}=\dfrac{23,2}{232}=0,1\left(mol\right)\\ \Rightarrow n_{O_2}=2n_{Fe_3O_4}=0,2\left(mol\right)\\ \Rightarrow V_{O_2\left(đktc\right)}=0,2\cdot22,4=4,48\left(l\right)\\ c,n_{Fe}=3n_{Fe_3O_4}=0,3\left(mol\right)\\ \Rightarrow m=m_{Fe}=0,3\cdot56=16,8\left(g\right)\)