If a 3.00-l flask contains 0.400 mol of co2 and 0.100 mol of o2 at equilibrium, how many moles of co are also present in the flask?

When the balanced equation for this reaction is:
2CO(g) + O2(g)→ 2CO2(g)
and according to Kc formula = concentration of the products/concentration of the reactant
Kc = [CO2]^2 / [CO]^2 [O2]
by getting the concentration of CO2 = 0.4 (no.of moles) / 3 (volume per L ) =0.13
and the concentration of O2 = 0.1 (no.of moles of O2) / 3 (volume per L)=0.03
and we have Kc value (given) = 1.4 x 10^2 
So by substitution in the Kc formula:
1.4x10^2 = 0.13^2 / [Co]^2 * 0.03
 
[CO]^2 = 0.13^2 / (1.4x10^2 * 0.03)= 0.004
[CO]= √0.004=  0.63 
that means moles of CO = 0.63 x 3 (volume L) = 1.89 moles

The use of piers and beams to build a strong foundation for a house.