Answer:
Kc = 1.35x10^7
Explanation:
Let's write the reaction again:
2R + A <------> 2Z Kp = 5.51x10^5
In order to know the value of Kc, we need to write the expression that relations the Kp with Kc which is:
Kp = Kc * (RT)^Δn (1)
Where:
R: 0.082 L atm/ K mol
Δn: difference between the coefficients of the reaction
Kc: equilibrium constant
T: temperature in K
Now, from the equation (1) we can solve for Kc:
Kc = Kp / (RT)^Δn (2)
Now, before do any calculations, let's do first the value of Δn:
Δn = 2 - (2+1) = -1
Now, replacing all values in (2):
Kc = 5.51x10^5 / (0.082*298)^-1
Kc = 1.346x10^7
The third option is the correct one.