equlibrium concentration

[theedaddy77]

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What is the equilibrium constant, K, at 400K if 3.00 moles of CO2(g) introduced into a 2 liter container are 20.0% dissociated at equilibrium?
2 CO2(g) <==> 2CO(g) + O2(g)




A. (0.30)2(0.15) / (1.20)2 mol/liter
B. (1.20)2 / (0.30)2(0.15) mol/liter


i know it is either or A or B but how do i know what is the product and was the reactant, when it is a equalibrium and can go both ways?

(the answer is A)

 

[Orgodox]

Dont over-think it even though its equilibrium generally refer to products on the left side and reactants on the right