The rate of effusion is inversely proportional to the molecular weight.
The molecular weight of krypton is 83.8.
1.161=√83.8M
M=62.27
Thus, the average molecular weight of the mixture of Cl2 and Cl is 62.27.
Let x be the mole fraction of Cl2. The mole fraction of Cl will be 1−x.
Hence, 71x+35.5(1−x)=62.27
x=0.754
The mole fractions of Cl2 and Cl are 0.754 and 0.246 respectively. They are also equal to the partial pressures as total pressure is 1 atm.
Kp=PCl2PCl2=0.24620.754=0.08
As Δn=1, KP=Kc(RT)
Thus, 0.08=Kc(0.082×1473)
Kc=6.71×10−4