Solution :-
Balanced reaction equation
Volume is 1 L so moles is nothing but the molarity for each
  CO    +    Br2
<----- > COBr2
0.500 MÂ Â Â Â Â 0.400
MÂ Â Â Â Â Â Â Â 0
-x                 Â
-x             Â
+x
0.500-x        Â
0.400-x      0.233M
Value of x= 0.233 M
So lets calculate the equilibrium concentration of the CO and
Br2
[CO]eq = 0.500 –x = 0.500 – 0.233 = 0.267 M
[Br2]eq = 0.400 –x = 0.400 – 0.233 = 0.167 M
Now lets calculate the equilibrium constant
Kc= [COBr2]/[CO]/[Br2]
Lets put the values in the formula
Kc = [0.233]/[0.267][0.167]
Kc= 5.23
So the equilibrium constant is 5.23
