When 20 g of CaCO₃ were put into 10 litre flask and heated to 800°C, 30% of CaCO₃ remained unreactable equilibrium. KP for decompostion of CaCO₃ will be___________.
A. 1.145 atm
B. 1.231 atm
C. 2.145 atm
D. 3.145 atm