Mass of Fe₂O₃ : 74.26 g
Volume of O₂ at STP = 15.624 L
<h3>Further explanation</h3>
Reaction
4Fe (s) + 3O₂ (g) ==> 2Fe₂O₃ (s)
mol Fe :
Ar Fe = 56 g/mol

mol Fe₂O₃ :

mass Fe₂O₃ :
MW Fe₂O₃ : 159,69 g/mol

mol O₂ :

volume O₂ at STP(1 mol=22.4 L)

For the reaction;
N2(g) + O2(g) = 2NO(g)
Kp = pNO²/ pN₂pO₂; (No units)
where;
pNO is the partial pressure of NO;
pN₂ is the partial pressure of nitrogen
pO₂ is the partial pressure of Oxygen
The equilibrium constant Kp is deduced from the balanced chemical equation for a reversible reaction, NOT experimental data as is the case for rate expressions in kinetics.
Kp changes with temperature considerably changing the position of an equilibrium, and, at a constant temperature, and therefore constant K, the position of an equilibrium can change significantly depending on relative concentrations/pressures of 'reactants' and 'products'.
I believe the answer is mass :)