An equilibrium mixture of O2, SO2 and SO3 contains equal concentrations of SO2 and SO3.
Calculate the concentration of O2 if Kc = 270 for the reaction: 2 SO2(g) + O2(g) - 2 SO3(0)

[O₂(g)] = 0.0037M

Explanation:

            2SO₂(g) + O₂(g) => 2SO₃(g)

Conc:   [SO₂(g)]   [O₂(g)]     [SO₃(g)]  and  [SO₂(g)] = [SO₃(g)]

Kc =  [SO₃(g)]²/[O₂(g)][SO₂(g)]² => Kc = 1/[O₂(g)] = 270 if [SO₂(g)] = [SO₃(g)]

∴ [O₂(g)] = (1/270)M = 0.0037M  

c (diamond),

sio2 (quartz)