PCl5, PCl3, and Cl2 are at equilibrium at 500 K in a closed container and their concentrations are 0.8×10-3 mol L-1 , 1.2×10-3 mol L-1 and 1.2×10-3 mol L-1, respectively.
The value of  Kc  for the reaction PCl5(g) ⇌ PCl3(g) + Cl2(g) will be:

1. 1.8 × 103 mol L-1 2. 1.8 × 103
3. 1.8 × 10-3 mol L-1 4. 0 . 55 × 104

Hint: The formula of Kc=[PCl3][Cl2][PCl5]
Step 1:
For the reaction, PCl5(g)PCl3(g)+Cl2(g)
The given values are as follows:
At 500 K in a closed container, [PCl5]=0.8×10-3 mol L-1
[PCl3]=1.2×10-3 mol L-1
[Cl2]=1.2×10-3 mol L-1
Step 2:
Kc=[PCl3][Cl2][PCl5]
=(1.2×10-3)×(1.2×10-3)(0.8×10-3)
=1.8×10-3