A 20-litre container at 400 K contains CO2(g) at pressure 0.4 atm and an excess of SrO (neglect the volume of solid SrO). The volume of the container is now decreased by moving the movable piston fitted in the container. The maximum volume of the container, when pressure of CO2 attains its maximum value, will be: (Given that: SrCO3(s)⇌SrO(s) + CO2(g), Kp = 1.6 atm)

The initial pressure PCO2 = 0.4 atm
The reaction is SrCO3(s) ⇌ SrO(s) + CO2(g)
Kp = PCO2 = 1.6 atm
When the pressure of CO2 reaches its maximum value, it will be equal to Kp.
Therefore, the maximum pressure of CO2 is 1.6 atm.
Let the initial volume be V1 = 20 L and the initial pressure be P1 = 0.4 atm.
Let the final volume be V2 and the final pressure be P2 = 1.6 atm.
Assuming the temperature remains constant, we can use Boyle's Law:
P1V1 = P2V2
0.4 atm × 20 L = 1.6 atm × V2
V2 = (0.4 atm × 20 L) / 1.6 atm
V2 = 5 L
Therefore, the maximum volume of the container when the pressure of CO2 attains its maximum value will be 5 liters.