K for the given reaction can be written as,
K = [CO2][CF4]/[COF2]^2
ICE table
                      Â
2COF2 <=====> CO2Â Â +Â Â Â CF4
Initial               2.00M                  Â
0Â Â Â Â Â Â Â Â Â Â Â Â Â Â
0
change            Â
2x                      Â
x             Â
x
equilibrium    Â
(2-2x)Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
x             Â
x
Feed the values,
8.60 = x^2/(2-2x)^2
Solve for x,
x = 0.85434 M
So, the equilibrium concentration of COF2 = 2.00 - 2 x 0.85434 =
0.29132 M (or 0.30 M)
